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Wilhelm M. Wundt (1832-1920)

1897 Outlines of Psychology. Grundriss der Psychologie, translated into English by C.H. Judd.

§1. Problem of Psychology
§2. General Theories of Psychology
§3. Methods of Psychology
§4. General Survey of the Subject

One: Psychical Elements
§5. Chief Forms and General Attributes of Psychical Elements
§6. Pure Sensations
§7. Simple Feelings

Two: Psychical Compounds
§8. Definition and Classification of Psychical Compounds
§9. Intensive Ideas
§10. Spacial Ideas
§11. Temporal Ideas
§12. Composite Feelings
§13. Emotions
§14. Volitional Processes

Three: Interconnections of Psychical Compounds
§16. 15. Consciousness and Attention
§16. Associations
§17. Apperceptive Combinations
§18. Psychical States

Four: Psychical Developments
§19. Psychical Attributes of Animals
§20. Psychical Development of the Child
§21. Development of Mental Communities

Five: Psychical Causality and Its Laws
§22. Concept of Mind
§23. Psychological Laws of Relations
§24. Psychological Laws of Development

Outlines of Psychology
Wilhelm Max Wundt (1897)
Translated by Charles Hubbard Judd (1897)

Wundt argues that a scientific observation involves (at the same time) the subjective inner sense of experience and the objective outer sense of what is observed through the senses.

A natural science, such as astronomy, concentrates on the outer sense and neutralises the subjective sense. Psychology is concerned with both. One way this can be done experimentally is to use simple sources of outer sensation (a simple musical tone, for example) and trained observers to report their subjective experience of it. In this way, the laws which regulate everyone's perceptions may be discovered.


1. Two definitions of psychology have been the most prominent in the history of this science. According to one, psychology is the "science of mind", psychical processes being regarded as phenomena from. which it is possible to infer the nature of an underlying metaphysical mind substance. According to the other, psychology is the "science of inner experience"; psychical processes are here looked upon as belonging to a specific form of experience, which is readily distinguished by the fact that its contents are known through "introspection", or through the "inner sense" as it is called if one uses the phrase phrase which has been employed to distinguish introspection from sense-perception through the outer senses.

Neither of these definitions, however, is satisfactory to the psychology of today. The first or metaphysical definition belongs to a period of development that lasted longer in this science than in others. But is here, too, forever left behind, since psychology has developed into an empirical discipline, operating with methods of its own; and since the "mental sciences" have gained recognition as a great department of scientific investigation, distinct from the sphere the natural sciences, and requiring as a general groundwork an independent psychology, free from all metaphysical theories.

[p. 2] The second or empirical definition, which sees in psychology a "science of inner experience", is inadequate because it may give rise to the misunderstanding that psychology has to do with objects totally different from the objects of so called "outer experience". It is, indeed, true that there are certain contents of experience which belong in the sphere of psychological investigation, and are not to be found among the objects and processes studied by natural science; such are our feelings, emotions, and decisions. On the other hand, there is not a single natural phenomenon that may not, from a different point of view, become an object of psychology. A stone, a plant, a tone, a ray of light, are, when treated as natural phenomena, objects of mineralogy, botany, physics, etc. In so far, however, as they are at the same time ideas, they are objects of psychology, for psychology seeks to account for the genesis of these ideas, and for their relations, both to other ideas and to those psychical processes, such as feelings, volitions, etc., which are not referred to external objects. There is then, no such thing as an "inner sense" which can be regarded as an organ of introspection, and as distinct from the outer senses, or organs of objective perception. The ideas of which psychology seeks to investigate the attributes, are identical with those upon which natural science is based; while the subjective activities of feeling, emotion, and volition, which are neglected in natural science, are not known through special organs but are directly and inseparably connected with the ides referred to external objects.

2. It follows, then, that the expressions outer and inner experience do not indicate different objects, but different points of view from which we take up the consideration and scientific treatment of a unitary experience. We are naturally led to these points of view, because every concrete ex-[p. 3]perience immediately divides into two factors: into a content presented to us, and our apprehension of this content. We call the first of these factors objects of experience, the second, experiencing subject. This division indicates two directions for the treatment of experience. One is that of the natural sciences, which concern themselves with the objects of experience, thought of as independent of the subject. The other is that of psychology, which investigates the whole content of experience in its relations to the subject and also in regard to the attributes which this content derives directly from the subject. The point of view of natural science may, accordingly, be designated as that of mediate experience, since it is possible only after abstracting from the subjective factor present in all actual experience; the point of view of psychology, on the other hand, may be designated as that of immediate experience, since it purposely does away with this abstraction and all its consequences.

3. The assignment of this problem to psychology, making it a general, empirical science coordinate with the natural sciences, and supplementary to them, is justified by the method of all the mental sciences, for which psychology furnishes the basis. All of these sciences, philology, history and political and social science, have as their subject matter, immediate experience as determined by the interaction of objects with knowing and acting subjects. None of the mental sciences employs the abstractions and hypothetical supplementary concepts of natural science; quite otherwise, they all accept ideas and the accompanying subjective activities as immediate reality. The effort is then made to explain the single components of this reality through their mutual interconnections. This method of psychological interpretation employed in each of the special mental sciences, must also be the mode of procedure in psychology itself, being the method required by the subject-matter of psychology, the immediate reality of experience.

[p. 4] Since natural science investigates the content of experience after abstracting from the experiencing subject, its problem is usually stated as that of acquiring "knowledge of the outer world". By the expression outer world is meant the sum total of all the objects presented in experience. The problem of psychology has sometimes been correspondingly defined as "self knowledge of the subject". This definition is, however, inadequate, because the interaction of the subject with the outer world and with other similar subjects is just as much a part of the problem of psychology as are the attributes of the single subject. Furthermore, the expression can easily be interpreted to mean that the outer world and the subject are separate components of experience, or, at least, components which can be distinguished as independent contents of experience, whereas, in truth, outer experience is always connected with the apprehending and knowing functions of the subject, and inner experience always contains ideas from the outer world as indispensable components. This interconnection is the necessary result of the fact that in reality experience is not a mere juxtaposition of different elements, but a single organized whole which requires in each of its components the subject which apprehends the content, and the objects which are presented as content. For this reason natural science can not abstract from the knowing subject entirely, but only from those attributes of the subject which either disappear entirely when we remove the subject in thought, as, for example, the feelings, or from those attributes which must be regarded on the ground of physical researches as belonging to the subject, as, for example, the qualities of sensations. Psychology, on the contrary, has as its subject of treatment the total, content of, experience in its immediate character.

The only ground, then, for the division between natural, science on the one hand, and psychology and the mental sciences on the other, is to be found in the fact that all in the fact that all experience contains as its factors a content objectively presented, and an experiencing subject. Still, it is by no means necessary that logical definitions of these two factors should precede the separation of the sciences from one another, for it is obvious that such definitions are possible only after they have a basis in the investigations of natural science and of psychology. All that it is [p. 5] necessary to presuppose from the first is the consciousness which accompanies all experience, that in this experience objects are being presented to a subject. There can be no assumption knowledge of the conditions upon which the distinction is based, or of the definite characteristics by which one factor is to be distinguished from the other. Even the use of the terms object and subject in this connection must be regarded as the application to the first stage of experience, of distinctions which are reached only through developed logical reflection.

The forms of interpretation in natural science and psychology are supplementary, not only in the sense that the first considers objects after abstracting, as far as possible, from the subject, while the second has to do with the part which the subject plays in the rise of experience; but they are also supplementary in the sense that each takes a different point of view in considering any single content of experience. Natural science seeks to discover the nature of objects without reference to the subject. The knowledge that it produces is therefore mediate or conceptual. In place of the immediate objects of experience, it sets concepts gained from these objects by abstracting from the subjective components of our ideas. This abstraction makes it necessary continually to supplement reality with hypothetical elements. Scientific analysis shows that many components of experience -- as, for example, sensations - are subjective effects of objective processes. These objective processes in their objective character, independent of the subject, can therefore never be a part of experience. Science makes up for this lack of direct contact with the objective processes, by forming supplementary hypothetical concepts of the objective properties of matter. Psychology, on the other hand, investigates the contents of experience in their complete and actual form, both the ideas that are referred to objects, and also the subjective processes which cluster about these ideas. The knowledge thus gained in psychology is, therefore, immediate and perceptual, -- perceptual in the broad sense of the term in which, not only sense perceptions, but all concrete reality is distinguished from all that is abstract and conceptual in thought. Psychology can exhibit the interconnection of the contents of experience, as these interconnections are actually presented to the subject, only by avoiding entirely the abstractions and supplementary concepts of natural science. Thus, while natural science and psychology are [p. 6] both empirical sciences in the sense that they aim to explain the contents of experience, though from different points of view, it is obvious that, in consequence of the special character of its problem, psychology must be recognized as the more strictly empirical.


1.. The view that psychology is an empirical science which deals, not with a limited group of specific contents of experience, but with the immediate contents of all experience, is of recent origin. It encounters even in the science of today hostile views, which are to be looked upon, in general, as the survivals of earlier stages of development, and which are in turn arrayed against one another according to their attitudes on the question of the relations of psychology to philosophy and to the other sciences. On the basis of the two definitions mentioned above (sec.1, 1) as being the most widely accepted, two chief forms of psychology may be distinguished: metaphysical psychology and empirical psychology. Each is further divided into a number of special tendencies.

Metaphysical psychology generally values very little the empirical analysis and causal interpretation of psychical processes. Regarding psychology as a part of philosophical metaphysics, the chief effort of such psychology is directed toward the discovery of a definition of the "nature of mind" which shall be in accord with the metaphysical system to which the particular form of psychology belongs. After a metaphysical concept of mind has thus been established, the attempt is made to deduce from it the actual content of psychical experience. The characteristic which distinguishes metaphysical psychology from empirical psychology, then, is its attempt to deduce psychical processes, not from other psychical processes, but from some [p. 7] substratum entirely unlike these processes themselves: either from the manifestations of a special mind­substance, or from the attributes and processes of matter. At this point metaphysical psychology branches off in two directions. Spiritualistic psychology considers psychical the manifestations of a specific mind­substance, which is regarded either as essentially different form matter (dualism), or as related in nature to matter (monism or monadalogy). The fundamental metaphysical doctrine of spiritualistic psychology is the assumption of the supersensible nature of mind, and in connection with this, the assumption of its immortality. Sometimes the further notion of preexistence is also added. Materialistic psychology, on the other hand refers psychical processes to the same material substratum as that which natural science employs for the hypothetical explanation of natural phenomena. According to this view, psychical processes, like physical vital processes, are connected with certain organizations of material particles which are formed during the life of the individual and broken up at the end of that life. The metaphysical character of this form of psychology is determined by its denial that the mind is supersensible in its nature as is asserted by spiritualistic psychology. Both theories have this in common, that they seek not to interpret psychical experience from experience itself, but to derive it from presuppositions about hypothetical processes in a metaphysical substratum.

2. From the strife that followed these attempts at metaphysical explanation, empirical psychology arose. Wherever empirical psychology is consistently carried out, it strives either to arrange psychical processes under general concepts derived directly from the interconnection of these processes themselves, or it begins with certain, as a rule simpler processes, and then explains the more complicated as the result of the interaction of those with which it started. There may be various fun-[p. 8] damental principles for such an empirical interpretation, and thus it becomes possible to distinguish several varieties of empirical psychology. In general, these may be classified according to two principles of division. The first has reference to the relation of inner and outer experience and to the attitude which the two empirical sciences, natural science and psychology, take toward each other. The second had reference to the facts or concepts derived from these facts, which are used for the interpretation of psychical processes. Every system of empirical psychology takes its place under both of these principles of classification.

3. On the general question as to the nature of psychical experience the two views already mentioned. (sec. 1) on account of their decisive significance in determining the problem of psychology: psychology of the inner sense, and psychology as the science of immediate experience. The first treats psychical processes as contents of a sphere of experience coordinate with the sphere of experiences which, derived through the outer senses, is assigned as the province of the natural sciences, but though coordinate is totally different from it. The second recognizes no real difference between inner and outer experience, but finds the distinction only in the different points of view from which unitary experience is considered in the two cases.

The first of these two varieties of empirical psychology is the older. It arose primarily through the effort to establish the independence of psychical observation in opposition to the encroachments of natural philosophy. In thus coordinating natural science and psychology, it sees the justification for the equal recognition of both spheres of science in the fact that they have entirely different objects and modes of perceiving these objects. This view has influenced empirical psychology in two ways. First, it favored the opinion that psychology should employ empirical [p. 9] methods, but that these methods, like psychological experience, should be fundamentally different from those of natural science. Secondly, it gave rise to the necessity of showing some connection or other between these two kinds of experience, which were supposed to be different. In regard to the first demand, it was chiefly the psychology of the inner sense that developed the method of pure introspection (sec. 3, 2). In attempting to solve the second problem, this psychology was necessarily driven back to a metaphysical basis, because of its assumption of a difference between the physical and the psychical contents of experience. For, from the very nature of the case, it is impossible, to account for the relations of inner to outer experience, or the so called "interaction between body and mind", from the position here taken, except through metaphysical presuppositions. These presuppositions must then, in turn, affect the psychological investigation itself in such a way as to result in the importation of metaphysical hypotheses into it.

4. Essentially distinct from the psychology of the inner sense is the form of psychology which defines itself as "the science of immediate experience". Regarding, as it does, outer and inner experience, not as different parts of experience, but as different ways of looking at one and the same experience, this form of psychology can not admit any fundamental difference between the methods of psychology and those of natural science. It has, therefore, sought above all to cultivate experimental methods which shall lead to just such an exact analysis of psychical processes as that which the explanatory natural sciences undertake in the case of natural phenomena, the only differences being those which arise from the diverse points of view. It holds, also, that the special mental sciences which have to do with concrete mental processes and creations, stand on the same basis of a scientific consideration of the immediate contents of [p. 10] experience and of their relations to acting subjects. It follows, then, that psychological analysis of the most general mental products, such as language, mythological ideas, and laws of custom, is to be regarded as an aid to the understanding of all the more complicated psychical processes. In its methods, accordingly, this form of psychology stands in close relation to other sciences: as experimental psychology, to the natural sciences; as social psychology, to the special mental sciences.

Finally, from this point of view, the question of the relation between psychical and physical objects disappears entirely. They are not different objects at all, but one and the same content of experience, looked at in one case -- that of the natural sciences -- after abstracting from the subject, in the other -- that of psychology -- in their immediate character and complete relation to the subject. All metaphysical hypotheses as to the relation of psychical and physical objects are, when viewed from this position, attempts to solve a problem which never would have existed if the case had been correctly stated. Though psychology must then dispense with metaphysical supplementary hypotheses in regard to the interconnection of psychical processes, because these processes are the immediate contents of experience, still another method of procedure, however, is open since inner and outer experience are supplementary points of view. Wherever breaks appear in the interconnection of psychical processes, it is allowable to carry on the investigation according to the physical methods of considering these same processes, in order to discover whether the absent link can be thus supplied. The same holds for the reverse method of filling up the breaks in the continuity of our physiological knowledge, by means of elements derived from psychological investigation. Only on the basis of such a view, which sets the two forms of knowledge in their true relation, is it, possible for psycholo-[p. 11]gy to become in the fullest sense an empirical science. Only in this way, too, can physiology become the true supplementary science of psychology, and psychology, on the other hand, the auxiliary of physiology.

5. Under the second principle of classification mentioned above (2), that is, according to the facts or concepts with which the investigation of psychical processes starts, there are two varieties of empirical psychology to be distinguished. They are, at the same time, successive stages in the development of psychological interpretation. The first corresponds to a descriptive, the second to an explanatory stage. The attempt to present a discriminating description of the different psychical processes, gave rise to the need of an appropriate classification. Class­concepts were formed, under which the various processes were grouped; and the attempt was made to satisfy the need of an interpretation in each particular case, by subsuming the components of a given compound process under their proper class­concepts. Such concepts are, for example, sensation, knowledge, attention, memory, imagination, understanding, and will. They correspond to the general concepts of physics which are derived from the immediate perception of natural phenomena, such as weight, heat, sound, and light. Like those concepts of physics, these derived psychical concepts may serve for a first grouping of the facts, but they contribute nothing whatever to the explanation of these facts. Empirical psychology has, however, often been guilty of confounding this description with explanation. Thus, the faculty-psychology considered these class­concepts as psychical forces or faculties, and referred psychical processes to their alternating or united activity.

6. Opposed to this method of treatment found in descriptive faculty psychology, is that of explanatory psychology. When consistently empirical, the latter must base its inter-[p. 12]pretations on certain facts which themselves belong to psychical experience. These facts may, however, be taken from different spheres of psychical activity, and so it comes that explanatory treatment may be further divided into two varieties which correspond respectively to the two factors, objects and subject, which go to make up immediate experience. When the chief emphasis is laid on the objects of immediate experience, intellectualistic psychology. This type of psychology attempts to derive all psychical processes, especially the subjective feelings, impulses, and volitions, from ideas, or intellectual processes as they may be called on account of their importance for knowledge of the objective world. If, on the contrary, the chief emphasis is laid on the way in which immediate experience arises in the subject, a variety of explanatory psychology results which attributes to those subjective activities referred to external objects, a position as independent as that assigned to ideas. This variety has been called voluntaristic psychology, because of the importance that must be conceded to volitional processes in comparison with other subjective processes.

Of the two varieties of psychology which result from the general attitudes on the question of the nature of inner experience (3), psychology of the inner sense commonly tends towards intellectualism. This is due to the fact that, when the inner sense is coordinated with the outer senses, the contents of psychical experience which first attract consideration are those which are presented as objects to this inner sense in a manner analogous to the presentation of natural objects to the outer senses. It is assumed that the character of objects can be attributed to ideas alone of all the contents of psychical experience, because they are regarded as images of the external objects presented to the outer senses. Ideas are, accordingly, looked upon as the only real objects of the inner sense while all processes not referred to external objects, as, [p. 13] for example, the feelings, are interpreted as obscure ideas, or as ideas related to one's own body, or, finally, as effects arising from combinations of ideas.

The psychology of immediate experience (4), on the other hand, tends toward voluntarism. It is obvious that here, where the chief problem of psychology is held to be the investigation of the subjective rise of all experience, special attention will be devoted to those factors from which natural science abstracts.

7. Intellectualistic psychology has in the course of its development separated into two trends. In one, the logical processes of judgment and reasoning are regarded as the typical forms of all psychoses; in the other, certain combinations of successive memory-images distinguished by their frequency, the so­called associations of ideas, are accepted as such. The logical theory is most clearly related to the popular method of psychological interpretation and is, therefore, the older. It still finds some acceptance, however, even in modern times. The association-theory arose from the philosophical empiricism of the last century. The two theories stand to a certain extent, in antithesis, since the first attempts to reduce the totality of psychical processes to higher, while the latter seeks to reduce it to the lower and, as it is assumed, simpler forms of intellectual activity. Both are one­sided, and not only fail to explain affective processes and volitional processes on the basis of the assumption with which they start, but are not able to give a complete interpretation even of the intellectual processes.

8. The union of psychology of the inner sense with the intellectualistic view has led to a peculiar assumption that has been in many cases fatal to psychological theory. We may define this assumption briefly as the erroneous attribution of the nature of things to ideas, to ideas. Not only was an analogy [p. 14] assumed between the objects of so­called inner sense and those of the outer senses, but former were regarded as the images of the latter; it came that the attributes which natural science ascribes to external objects, were also transferred to the immediate objects of the "inner sense", the ideas. The assumption was made that ideas are themselves things, just as the external objects to which we refer them; that they disappear from consciousness and come back into it; that they may, indeed, be more or less intensely and clearly perceived, according as the inner sense is stimulated through the outer senses or not, and according to the degree of attention concentrated upon them, but that on the they remain unchanged in qualitative character.

9. In all these respects voluntaristic psychology is opposed to intellectualism. While the latter assumes an inner sense and specific objects of inner experience, volunteerism is closely related to the view that inner experience is identical with immediate experience. According to this doctrine, the content psychological experience does not consist of a sum of objects, but of all that which makes up the process of experience in general, that is of all the experiences of the subject in their immediate character, unmodified by abstraction or reflection. It follows of necessity that the contents of psychological experience are here regarded as an interconnection of processes.

This concept of process excludes the attribution of an objective and more or less permanent character to the contents of psychical experience. Psychical facts are occurrences, not objects; they take place, like all occurrences, in time and are never the same at a given point in time as they were during the preceding moment. In this sense volitions are typical for all psychical porcesses. Voluntaristic psychology does not by any means assert that volition is the only real form of psychosis, but merely that, with its closely related [p. 15] feelings and emotions, it is just as essential a component of psychological experience as sensations and ideas. It holds, further, that all other psychical processes are to be thought of after the analogy of volitions, they too being a series of continuous changes in time, not a sum of permanent objects, as intellectualism generally assumes in consequence of its erroneous attribution to ideas of those properties which we attribute to external objects. The recognition of the immediate reality of psychological experience excludes the possibility of the attempt to derive the particular components of psychical phenomena from any others specifically different. The analogous attempts of metaphysical psychology to reduce all psychological experience to the heterogeneous, imaginary processes of a hypothetical substratum are, for the same reason, inconsistent with the real problem of psychology. While it concerns itself, however, with immediate experience, psychology assumes from the first that all psychical contents contain objective as well a subjective factors. These are to be distinguished only through deliberate abstraction, and can never appear as really separate processes. In fact, immediate experience shows that there are no ideas which do not arouse in us feelings and impulses of different intensities, and, on the other hand, that a feeling or volition is impossible which does not refer to some ideated object.

10. The governing principles of the psychological position maintained in the following chapters may be summed up in three general statements.

1) Inner, or psychological experience is not a special sphere of experience apart from others, but is immediate experience in its totality.

2) This immediate experience is not made up of unchanging contents but of an interconnection of processes; not of objects, but of occurrences, of universal human experiences and their relations in accordance with certain laws.

[p. 16] 3) Each of these processes contains an objective content and a subjective process, thus including the general conditions both of all knowledge and of all practical human activity.

Corresponding to these three general principles, we have a threefold relation of psychology to the other sciences.

1) As the science of immediate experience, it is supplementary to the natural sciences, which, in consequence of their abstraction from the subject, have to do only with the objective, mediate contents of experience. Any particular fact can, strictly speaking, be understood in its full significance only after it has been subjected to the analyses of both natural science and psychology. In this sense, then, physics and physiology are auxiliary to psychology, and the latter is, in turn, supplementary to the natural sciences.

2) As the science of the universal forms of immediate human experience and their combination in accordance with certain laws, it is the foundation of the mental sciences. The subject-matter of these sciences is in all cases of the activities proceeding from immediate human experiences, and their effects. Since psychology has for its problem the investigation of the forms and laws of these activities, it is at once the most, general mental science, and the foundation for all the others, such as philology, history, political economy, jurisprudence, etc.

3) Since psychology pays equal attention to both the subjective and objective conditions which underlie not only theoretical knowledge, but practical activity as well, and since it seeks to determine their interrelation, it is the empirical discipline whose results are most immediately useful in the invention of the general problems of the theory of knowledge, and ethics, the two foundations of philosophy. Thus, psychology is, in relation to the natural sciences, the supplementary, in relation to the mental sciences the fundamental, and [p. 17] in relation to philosophy it is the propaedeutic empirical science.

10a. The view that it is not a difference in the objects of experience, but in the way of treating experience, that distinguishes psychology from natural science has come to be recognized more and more in modern psychology. Still a clear comprehension of the essential charactor of this position in regard to the scientific problems of psychology, is prevented by the persistence of older tendencies derived from metaphysics and natural philosophy. Instead of starting from the fact that the natural sciences are possible only after abstracting from the subjective factors of experience, the more general problem of treating the contents of all experience in the most general way, is sometimes assigned to natural science. In such a case psychology is, of course, no longer coordinate with the natural sciences, but subordinate to them. Its problem is no longer to remove the abstraction employed by the natural sciences, and in this way to gain with them a complete view of experience, but it has to use the concept "subject" furnished by the natural sciences, and to give an account of the influence of this subject on the contents of experience. Instead of recognizing that an adequate definition of "subject" is possible only as a result of psychological investigations (sec. 1, 3a), a finished concept formed exclusively by the natural sciences is here foisted upon psychology. Now. for the natural sciences the subject identical with the body. Psychology is accordingly defined as the science which has to determine the dependence of immediate experience on the body. This position, which may be designated "psycho-physical materialism", is epistemologically untenable and psychologically unproductive. Natural science, which purposely abstracts from the subjective component of all experience, is at least in a position to give a final definition of the subject. A psychology that starts with such a purely physiological definition depends, therefore, not on experience but, just like the older materialistic psychology, on a metaphysical presupposition. The position is psychologically unproductive because, from the very first, it turns over the causal interpretation of psychical processes to physiology. But physiology has not yet furnished such an interpretation and never [p. 18] will be able to do so, because of the difference between the manner of regarding phenomena in natural science and in psychology. It is obvious, too, that such a form of psychology, which been turned into hypothetical brain-mechanics, con never be of any service as a basis for the mental sciences.

The strictly empirical trend of psychology, defined in the principles formulated above, is opposed to these attempts to renew metaphysical doctrines. In calling it "voluntaristic", we are not to overlook the fact that, in itself, this psychological voluntarism has absolutely no connection with any metaphysical doctrine of will. Indeed it stands in opposition to Schopenhauer's one-sided metaphysical voluntarism, which derived all from being from a transcendental original will, and to the metaphysical systems of a Spinoza or a Herbart, which arose from intellectualism. In its relation to metaphysics, the characteristic of psychological voluntarism in the sense above defined, is its exclusion of all metaphysics from psychology. In its relations to other forms of psychology, it refuses to accept any of the attempts to reduce volitions to mere ideas, and at the same time emphasizes the typical character of volition for all psychological experience. Volitional acts are universally recognized as occurrences, made up of a series of continual changes in quality and intensity. They are typical in the sense that this characteristic of being occurrences is held to he true for all the contents of psychical experience.


1. Since psychology has for its object, not specific contents of experience, but general experience in its immediate character, it can make use of no methods except such as the empirical sciences in general employ for the determination, analysis, and causal synthesis of facts. The circumstance, that natural science abstracts from the subject, while psychology does not, can be no ground for modifications in the essential character of the methods employed in the two fields, though it does modify the way in which these methods are applied. [p. 19]

The natural sciences, which may serve as an example for psychology in this respect, since they were developed earlier, make use of two chief methods: experiment and observation. Experiment is observation connected with an intentional interference on the part of the observer, in the rise and course of the phenomena observed. Observation, in its proper sense, is the investigation of phenomena without such interference, just as they are naturally presented to the observer in the continuity of experience. Wherever experiment is possible, it is always used in the natural sciences; for under all circumstances, even when the phenomena in themselves present the conditions for sufficiently exact observation, it is an advantage to be able to control at will their rise and progress, or to isolate the various components of a composite phenomenon. Still, even in the natural sciences the two methods have been distinguished according to their spheres of application. It is held that the experimental methods are indispensable for certain problems, while in others the desired end may not infrequently be reached through mere observation. If we neglect a few exceptional cases due to special relations, these two classes of problems correspond to the general division of natural phenomena into processes and objects.

Experimental interference is required in the exact determination of the course, and in the analysis of the components, of any natural process such as, for example, light-waves or sound-waves, an electric discharge, the formation or disintegration of a chemical compound, and stimulation and metabolism in plants and animals. As a rule, such interference is desirable because exact observation is possible only when the observer can determine the moment at which the process shall commence. It is also indispensable in separating the various components of a complex phenomenon from one another. As a rule, this [p. 20] is possible only through the addition or subtraction of certain conditions, or a quantitative variation of them.

The case is different with objects of nature. They are relatively constant; they do not have to be produced at a particular moment, but are always at the observer's disposal and ready for examination. Here, then, experimental investigation is generally necessary only when the production and modification of the objects are to be inquired into. In such a case, they are regarded either as products or components of natural processes and come under the head of processes rather than objects. When, on the contrary, the only question is the actual nature of these objects, without reference to their origin or modification, mere observation is generally enough. Thus, mineralogy, botany, zoology, anatomy, and geography, are pure sciences of observation so long as they are kept free from the physical, chemical, and physiological problems that are, indeed, frequently brought into them, but have to do with processes of nature, not with the objects in themselves.

2. If we apply these considerations to psychology, it is obvious at once, from the very nature of its subject-matter, that exact observation is here possible only in the form of experimental observation; and that psychology can never be a pure science of observation. The contents of this science are exclusively processes, not permanent objects. In order to investigate with exactness the rise and progress of these processes, their composition out of various components, and the interrelations of these components, we must be able first of all to bring about their beginning at will, and purposely to vary the conditions of the same. This is possible here, as in all cases, only through experiment, not through pure introspection. Besides this general reason there is another, peculiar to psychology, that does not apply at all to natural [p. 21] phenomena. In the latter case we purposely abstract from the perceiving subject, and under circumstances, especially when favored by the regularity of the phenomena, as in astronomy, mere observation may succeed in determining with adequate certainty the objective components of the processes. Psychology, on the contrary, is debarred from this abstraction by its fundamental principles, and the conditions for chance observation can be suitable only when the same objective components of immediate experience are frequently repeated in connection with the same subjective states. It is hardly to be expected, in view of the great complexity of psychical processes, that this will ever be the case. The coincidence is especially improbable since the very intention to observe, which is a necessary condition of all observation, modifies essentially the rise and progress of psychical processes. Observation of nature is not disturbed by this intention on the part of the observer, because here we purposely abstract from the state of the subject. The chief problem of psychology, however, is the exact observation of the rise and progress of subjective processes, and it can be readily seen that under such circumstances the intention to observe either essentially modifies the facts to be observed, or completely suppresses them. On the other hand, psychology, by the very way in which psychical processes originate, is led, just as physics and physiology are, to employ the experimental mode of procedure. A sensation arises in us under the most favorable conditions for observation when it is caused by an external sense-stimulus, as, for example, a tone-sensation from an external tone-vibration, or a light-sensation from an external light-impression. The idea of an object is always caused originally by the more or less complicated cooperation of external sense-stimuli. If we wish to study the way in which an idea is formed, we can choose [p. 22] no other method than that of imitating this natural process. In doing this, we have at the same time the great advantage of being able to modify the idea itself by changing at will the combination of the impressions that cooperate to form it, and of thus learning what influence each single condition exercises on the product. Memory-images, it is true, cannot be directly aroused through external sense impressions, but follow them after a longer or shorter interval. Still, it is obvious that their attributes, and especially their relation to the primary ideas through direct impressions, can be most accurately be learned, not by waiting for their chance arrival, but by using such memory-ideas as may be aroused in a systematic, experimental way, through immediately preceding impressions. The same is true of feelings and volitions; they will be presented in the form best adapted to exact investigation when those impressions are purposely produced which experience has shown to be regularly connected with affective and volitional reactions. There is, then, no fundamental psychical process to which experimental methods can not be applied, and therefore none in whose investigation they are not logically required.

3. Pure observation, such as is possible in many departments of natural science, is, from the very character of psychic phenomena, impossible in individual psychology. Such a possibility would be conceivable only under the condition that there existed permanent psychical objects, independent of our attention, similar to the relatively permanent objects of nature, which remain unchanged by our observation of them. There are, indeed, certain facts at the disposal of psychology, which, although they are not real objects, still have the character of psychical objects inasmuch as they possess these attributes of relative permanence, and independence of the observer. Connected with these characteristics [p. 23] is the further fact that they are unapproachable by means of experiment in the common acceptance of the term. These facts are the mental products that have been developed in the course of history, such as language, mythological ideas, and customs. The origin and development of these products depend in every case on general psychical conditions which may be inferred from their objective attributes. Psychological analysis can, consequently, explain the psychical processes operative in their formation and development. All such mental products of a general character presuppose as a condition the existence of a mental community composed of many individuals, though, of course, their deepest sources are the psychical attributes of the individual. Because of this dependence on the community, in particular the social community, this whole department of psychological investigation is designated as social psychology, and distinguished from individual, or as it may be called because of its predominating method, experimental psychology. In the present stage of the science these two branches of psychology are generally taken up in different treatises; still, they are not so much different departments as different methods. So-called social psychology corresponds to the method of pure observation, the objects of observation in this case being the mental products. The necessary connection of these products with social communities, which has given to social psychology its name, is due to the fact that the mental products of the individual are of too variable a character to be the subjects of objective observation. The phenomena gain the necessary degree of constancy only when they become collective.

Thus psychology has, like natural science, two exact methods: the experimental method, serving for the analysis of simpler psychical processes, and the observation of general [p. 24] mental products, serving for the investigation of the higher psychical processes and developments.

3a. The introduction of the experimental method into psychology was originally due to the modes of procedure in physiology, especially in the physiology of the sense-organs and the nervous system. For this reason experimental psychology is also commonly called "physiological psychology"; and works treating it under this title regularly contain those supplementary facts from the physiology of the nervous system and the sense-organs, which require special discussion with a view to the interests of psychology, though in themselves they belong to physiology alone. "Physiological psychology" is, accordingly, an intermediate discipline which is, however, as the name indicates, primarily psychology, and is, apart from the supplementary physiological facts that it presents, just the same as "experimental psychology" in the sense above defined. The attempt sometimes made, to distinguish psychology proper from physiological psychology, by assigning to the first the psychological interpretation of inner experience, and to the second the derivation of this experience from physiological processes, is to be rejected as inadmissible. There is only one kind of causal explanation in psychology, and that is the derivation of more complex psychical processes from simpler ones. In this method of interpretation physiological elements can be used only as supplementary aids, because of the relation between natural science and psychology as above defined (§ 2, 4). Materialistic psychology denies the existence of psychical causality, and substitutes for this problem the other, of explaining psychical processes by brain-physiology. This tendency, which has been shown (§ 2, 10a) to be epistemologically and psychologically untenable, appears among the representatives of both "pure" and "physiological" psychology.



1.  The concept "pure sensation" as shown in § 5 is the product of a twofold abstraction: 1) from the ideas in which the sensation appears, and 2) from the simple feelings with which it is united. We find that pure sensations, defined in this way, form a number of disparate systems of quality; each of these systems, such as that of sensations of pressure, of tone, or of light, is either a homogeneous or a complex continuity (§ 5, 5) from which no transition to any other system can be found.

2.  The rise of sensations, as physiology teaches us, is regularly dependent on certain physical processes that have their origin partly in the external world surrounding us, partly in certain bodily organs. We designate these processes with a name borrowed from physiology as sense-stimuli or sensation-stimuli. If the stimulus is a process in the outer world we call it physical; if it is a process in our own body we call it physiological. Physiological stimuli may be divided, in turn, into peripheral and central, according as they are processes in the various bodily organs outside of the brain, or processes in the brain itself. In many cases a sensation is attended by all three forms of stimuli. Thus, to illustrate, an external impression of light acts as a physical, stimulus on the eye; in the eye and optic nerve there arises a peripheral physiological stimulation; finally a central physiological stimulation takes place in the corpora quadrigemina and in the occipital regions of the cerebral cortex, where the optic nerve terminates. In many cases the physical stimulus may be wanting, while both forms of physiological stimuli are present; as, when we perceive a flash of light in consequence of a violent ocular movement. In still other cases the central stimulus alone is present; as, when we recall a light [p.39] impression previously experienced. The central stimulus is, accordingly, the only one that always accompanies sensation. When a peripheral stimulus causes a sensation, it must be connected with a central stimulus, and a physical must be connected with both a peripheral and a central stimulus.

3.  The physiological study of development renders it probable that the differentiation of the various sensational systems has been effected in part in the course of general development. The original organ of sense is the outer skin with the sensitive inner organs adjoining it. The organs of taste, smell, hearing, and sight, on the other hand, are later differentiations of it. It may, therefore, be surmised that the sensational systems corresponding to these special sense-organs, have also gradually arisen through differentiation from the sensational systems of the general sense, from sensations of pressure, hot, and cold. It is possible, too, that in lower animals some of the systems now so widely differentiated are even yet more alike. From a physiological standpoint the primordeal character of the general sense is also apparent in the fact that it has for the transfer of sense-stimuli to the nerves either very simple organs or none at all. Pressure, temperature, and pain-stimuli can produce sensations at points in the skin where, in spite of the most careful investigation, no special end-organs can be found. There are, indeed, special receiving organs in the regions most sensitive to pressure (touch-corpuscles, end-bulbs, and corpuscles of Vater), but their structure renders it probable that they merely favor the mechanical transfer of the stimulus to the nerve-endings. Special end-organs for hot, cold, and pain-stimuli have not been found at all.

In the later developed special sense-organs, on the other hand, we find everywhere structures which not only effect the suitable transfer of the stimuli to the sensory nerves, but generally bring about a physiological transformation of the [p. 40] stimulation which is indispensable for the rise of the peculiar sensational qualities. But even among the special senses there are differences in this respect.

The receiving organ in the ear, in particular, appears to be of a character different from that of the organs of smell, taste, and sight. In its most primitive forms it consists of a vesicle filled with one or more solid particles (otoliths), and supplied with nerve-bundles distributed in its walls. The particles are set in motion through sound-vibrations, and must cause a rapid succession of weak pressure-stimulations in the fibres of the nerve-bundles. The auditory organ of the higher animals shows an extraordinary complexity, still, in its essential structure it recalls this primitive type. In the cochlea of man and the higher animals the auditory nerve passes at first through the axis, which is pierced by a large number of fine canals, and then emerges through the pores which open into the cavity of the cochlea. Here the branches are distributed on a tightly stretched membrane, which extends through the spiral windings of the cochlea and is weighted with special rigid arches (arches of Corti). This membrane - the basilar membrane, as it is called - must, according to the laws of acoustics, be thrown into sympathetic vibrations whenever sound-waves strike the ear. It seems, therefore, to play the same part here as the otoliths do in the lower forms of the auditory organ. At the same time one other change has taken place which accounts for the enormous differentiation of the sensational system. The basilar membrane has a different breadth in its different parts, for it grows continually wider from the base to the apex of the cochlea. In this way it acts like a system of stretched chords of different lengths. And just as in such a system, other conditions remaining the same, the longer chords are tuned to lower and the shorter to higher tones, so we may assume the same to [p. 41] be true for the different parts of the basilar membrane. We may surmise that the simplest auditory organs with their otoliths have a homogeneous sensational system, analogous perhaps to our systems of sensations of pressure. The special development of the organ as seen in the cochlea of higher animals explains the evolution of an extraordinarily complex sensational system from this originally homogeneous system. Still, the structure remains similar in this respect, that it seems adapted, in the latter case as in the former, to the best possible transfer of the physical stimulus to the sensory nerve rather than to any transformation of the stimulus. This view agrees with the observed fact that, just as sensations of pressure may be perceived, on regions of the skin not supplied with special receiving organs, so, in the case of certain animals, such as birds, where the conditions are specially favorable for their transmission, sound-vibrations are transferred to the auditory nerve and sensed even after the removal of the whole auditory organ with its special receiving structure.

With smell, taste, and sight the case is essentially different. Organs are present which render direct action of the stimuli on the sensory nerves impossible. The external stimuli are here received through special organs and modified before they excite the nerves. These organs are specially metamorphosed epithelial cells with one end exposed to the stimulus and the other passing into a nerve fibre. Everything goes to show that the receiving organs here are not merely for the transfer of the stimuli, but rather for their transformation. In the three cases under discussion it is probable that the transformation is a chemical process. In smell and taste we have external chemical agencies, in sight we have light as the causes of chemical disintegrations in the sensory cells; these processes in the cells then serve as the real stimuli. [p. 42]

These three senses may, as chemical senses, be distinguished from the mechanical senses of pressure and sound. It is impossible to say with any degree of certainty, to which of these two classes sensations of cold and hot belong. One indication of the direct relation between stimuli and sensation in mechanical senses, as contrasted with the indirect relation in chemical senses, is that in the first case the sensation lasts only a very little longer than the external stimulus, while in the latter case it persists very much longer. Thus, in a quick succession of pressures and more especially of sounds, it is possible to distinguish clearly the single stimuli from one another; lights, tastes, and smells, on the other hand, run together at a very moderate rate of succession.

4.  Since peripheral and central stimuli are regular physical concomitants of elementary sensational processes, the attempt to determine the relation between stimuli and sensations is very natural. In attempting to solve this problem, physiology generally considers sensations as the result of physiological stimuli, but assumes at the same time that in this case any proper explanation of the effect from its cause is impossible, and that all that can be undertaken is to determine the constancy of the relations between particular stimuli, and the resulting sensations. Now, it is found in many cases that different stimuli acting on the same end-organ produce the same sensations; thus, for example, mechanical and electrical stimulations of the eye produce light sensations. This result was generalized in the principle, that every receiving element of a sense-organ and every simple sensory nerve-fibre together with its central terminus, is capable of only a single sensation of fixed quality; that the various qualities of sensation are, therefore, due to the various physiological elements with different specific energies.

This principle, generally called the "law of specific energy [p. 43] of nerves", is untenable for three reasons, even if we neglect for the moment the fact that it simply refers the causes of the various differences in sensations to a qualtalitas occutlta of sensory and nervous elements.

1) It is contradictory to the physiological doctrine of the development of the senses. If, as we must assume according to this doctrine, the complex sensational systems are derived from systems originally simpler and more homogeneous, the physiological sensory elements must have undergone a change also. This, however, is possible only under the condition that organs may be modified by the stimuli which act upon them. That is to say, the sensory elements determine the qualities of sensations only secondarily, as a result of the properties which they acquire through the processes of stimulation aroused in them. If, then, these sensory elements have undergone, in the course of time, radical changes due to the nature of the stimuli acting upon them, such changes could have been possible only under the condition that the physiological stimulations in the sensory elements varied to some extent with the quality of the stimulus.

2) The principle of specific energy is contradictory to the fact that in many senses the number of different sensory elements does not correspond at all to that of different sensational qualities. Thus, from a single point in the retina we can receive all possible sensations of brightness and color; in the organs of smell and taste we find no clearly distinguishable forms of the sensory elements, while even a limited area of their sensory surfaces can receive a variety of sensations, which, especially in the case of the olfactory organ, is very large. Where we have every reason to assume that qualitatively different sensations actually do arise in different sensory elements, as in the case of the auditory organ, the structure of the organ goes to show that this difference [p. 44] is not due to any attribute of the nerve-fibres or of other sensory elements, but that it comes originally from the way in which they are arranged. Different fibres of the auditory nerve will, of course, be stimulated by different tone-vibrations, because the different parts of the basilar membrane are tuned to different tones; but this is not due to some original and inexplicable attribute of the single auditory nerve-fibres, but to the way in which they are connected with the end-organ.

3) Finally, the sensory nerves and central elements can have no original specific energy, because the peripheral sense-organ must be exposed to the adequate stimuli for a sufficient interval, or must at least have been so exposed at some previous period, before the corresponding sensations can arise through their stimulation. Persons congenitally blind and deaf do not have any sensations of light or tone whatever, so far as we know, even when the sensory nerves and centres were originally present.

Everything goes to show that the differences in the qualities of sensations are conditioned by the differences in the processes of stimulation that arise in the sense-organs. These processes are dependent, primarily on the character of the physical stimuli, and only secondarily on the peculiarities of the receiving organ, which are due to its adaptation to these stimuli. As a result of this adaptation, however, it may happen that even when some stimulus other than that which has effected the original adaptation of the sensory elements, that is, when an inadequate stimulus acts, the sensation corresponding to the adequate stimulus may arise. Still, this does not hold for all stimuli or for all sensory elements. Thus, hot and cold stimulations can not cause cutaneous sensations of pressure or sensations in the special sense-organs; chemical and electrical stimuli produce sensations of light only when they act upon the retina, not when they act on [p. 45] the optic nerve; and, finally, these general stimuli can not arouse sensations of smell or taste. When an electric current causes chemical disintegration, it may, indeed, arouse such sensations, but it is through the adequate chemical stimuli produced.

5.  From the very nature of the case, it is impossible to explain the character of sensations from the character of physical and physiological stimuli. Stimuli and sensations can not be compared with one another at all; the first belong to the mediate experience of the natural sciences, the second to the immediate experience of psychology. An interrelation between sensations and physiological stimuli must necessarily exist, however, in the sense that different kinds of stimulation always correspond to different sensations. This principle of the parallelism of changes in sensation and in physiological stimulation is an important supplementary principle in both the psychological and physiological doctrines of sensation. In the first case it is used in producing definite changes in the sensation by means of intentional variation of the stimulus; in the second it is used in inferring the identity or non-identity of physiological stimulations from the identity or non-identity of the sensations. Furthermore, the same principle is the basis of our practical life and of our theoretical knowledge of the external world.


6.  The definition of the "general sense" includes two factors. In point of time, the general sense is that which precedes all others and therefore belongs to all beings, endowed with mind. In its spacial attributes, the general sense is distinguished from the particular senses in having the most extensive sensory surface exposed to stimuli. It includes not only the whole external skin and the adjoining areas of [p. 46] the mucous membrane, but a large number of internal organs supplied with sensory nerves, such as joints, muscles, tendons, and bones, which are accessible to stimuli either always, or at certain times, under special conditions, as is the case with bones. The general sense includes four specific, distinct sensational systems: sensations of pressure, hot, cold, and pain. Not infrequently a single stimulus arouses more than one, of these sensations. The sensation is then immediately recognized as made up of a mixture of components from the different systems; for example, from sensations of pressure and pain, or from sensations of hot and pain. In a similar manner as a result of the extension of the sense-organ, we may often have mixtures of the various qualities of one and the same system, for example, qualitatively different sensations of pressure, when an extended region of the skin is touched.

The four systems of the general sense are all homogenous systems (§ 5, 5). This shows that the sense is genetically earlier than the others, whose systems are all complex. The sensations of pressure from the external skin, and those due to the tensions and movements of the muscles, joints, and tendons, are generally grouped together under the name touch-sensations, and distinguished from the common sensations, which include sensations of hot, cold, and pain, and those sensations of pressure that sometimes arise in the other internal organs. This distinction, however, has its source in the relation of the sensations to ideas and concomitant feelings, and has nothing to do with the qualities of the sensations in themselves.

7.  The ability of the different parts of the general sense-organ to receive stimulations and give rise to sensations, can be tested with adequate exactness only on the external skin. The only facts that can be determined in regard to [p. 47] the internal parts, are that the joints are in a high degree sensitive to pressures, while the muscles and tendons are much less so, and that sensations of hot, cold, and pain in the internal organs are exceptional, and noticeable only under abnormal conditions. On the other hand, there is no point of the external skin and of the immediately adjoining parts of the mucous membrane, which is not sensitive at once to stimulations of pressure, hot, cold, and pain. The degree of sensitivity may, indeed, vary at different points, in such a way that the points most sensitive to pressure, to hot, and to cold, do not, in generally, coincide. Sensitivity to pain is everywhere about the same, varying at most in such a way that in some places the pain-stimulus acts on the surface, and in others not until it has penetrated deeper. On the other hand, certain approximately punctiform cutaneous regions appear to be most favorable for stimulations of pressure, hot, and cold. These points are called respectively, pressure-spots, hot-spots, and cold-spots. They are distributed in different parts of the skin in varying numbers. Spots of different modality never coincide; still, temperature-spots always receive sensations of pressure and pain as well; and a pointed hot stimulus applied to a cold spot, always causes a sensation of hot, while hot-spots do not seem to be stimulated by pointed cold stimuli. Furthermore, hot-spots and cold-spots react with their adequate sensations to properly applied mechanical and electrical stimuli.

8.  Of the four qualities mentioned sensations of pressure and pain form closed systems which show no relations either to each other or to the two systems of temperature-sensations. These last two, on the other hand, stand in the relation of opposites; we apprehend hot and cold not merely as different, but as contrasted sensations. It is, however, very probable that this is not due to the original nature of the sensations, [p. 48] but partly to the conditions of their rise, and partly to the accompanying feelings. For, while the other qualities may be united without limitation to form mixed sensations -- as, for example, pressure and hot, pressure and pain, cold and pain - hot and cold exclude each other because, under the conditions of their rise, the only possibilities for a given cutaneous region are a sensation of hot or one of cold, or else an absence of both. When one of these sensations passes continuously into the other, the change regularly takes place in such a way that either the sensation of hot gradually disappears and a continually increasing sensation of cold arises, or vice versa the sensation of cold disappears and that of hot gradually arises. Then, too, elementary feelings of opposite character are connected with hot and cold, the point where both sensations are absent corresponding to their indifferent zone.

In still another respect the two systems of temperature-sensations are peculiar. They are to a great extent dependent on the varying conditions under which the stimuli act upon the sense-organ. A considerable increase above the temperature of the skin is perceived as hot, while a considerable decrease below the same is perceived as cold, but the temperature of the skin itself, which is the indifference zone between the two, can adapt itself rapidly to the existing, external temperature within fairly wide limits. The fact that in this respect too, both systems are alike, favors the view that they are interconnected and also antagonistic.


9. We possess two independent systems of simple auditory sensations, which are generally, however, connected as a result of the mixture of the two kinds of impressions. They are [p. 49] the homogeneous system of simple noise-sensations and the complex system of simple tone-sensations.

Simple noise-sensations can be produced only under conditions that exclude the simultaneous rise of tonal sensations, as when air-vibrations are produced whose rate is either too rapid or too slow for tone-sensations to arise, or when the sound-waves act upon the ear for too short a period. Simple sensations of noise, thus produced, may vary in intensity and duration, but apart from these differences they are qualitatively alike. It is possible that small qualitative differences also exist among them, due to the conditions of their rise, but such differences are too small to be marked by distinguishing names. The noises commonly so called are compound ideas made up of such simple noise-sensations and of a great many irregular tonal sensations (cf. § 9, 7). The homogeneous system of simple noise-sensations is probably the first to develop. The auditory vesicles of the lower animals, with their simple otoliths, could hardly produce anything but these. In the case of man and the higher animals it may be surmised that the structures found in the vestibule of the labyrinth receive only homogeneous stimulations, corresponding to simple sensations of noise. Finally, experiments with animals deprived of their labyrinths, make it probable that even direct stimulations of the auditory nerve can produce such sensations (p. 41). In the embryonic development of the higher animals, the cochlea develops from an original, vestibular vesicle, which corresponds exactly to a primitive auditory organ. We are, therefore, justified in supposing that the complex system of tonal sensations is a product of the differentiation of the homogeneous system of simple noise-sensations, but that in every case where this development, has taken place, the simple system has remained along with the higher. [p. 50]

10. The system of simple tone-sensation is a continuity of one dimension. We call the quality of the single simple tones pitch. The one-dimensional character of the system finds expression in the fact that, starting with a given pitch, we can vary the quality only in two opposite directions: one we call raising the pitch, the other lowering it. In actual experience simple sensations of tone are never presented alone, but always united with other tonal sensations and with accompanying simple sensations of noise. But since, according to the scheme given above (§ 5, 1), these concomitant elements can be varied indefinitely, and since in many cases they are relatively weak in comparison with one of the tones, the abstraction of simple tones was early reached through the practical use of tonal sensations in the art of music. The names c, c#, d#, and d stand for simple tones, though the clangs of musical instruments or of the human voice by means of which we produce these different pitches, are always accompanied by other, weaker tones and often, too, by noises. But since the conditions for the rise of such concomitant tones can be so varied that they become very weak, it has been possible to produce really simple tones of nearly perfect purity. The simplest means of doing this is by using a tuning-fork, and a resonator tuned to its fundamental tone. Since the resonator increases the intensity of the fundamental only, the other, accompanying tones are so weak when the fork sounds, that the sensation is generally apprehended as simple and irreducible. If the sound-vibrations corresponding to such a tonal sensation are examined, they will be found to correspond to the simplest possible form of vibration, the pendulumoscillation, so called because the vibrations of the atmospheric particles follow the same laws as a pendulum oscillating in [p. 51] a very small amplitude. [1] That these relatively simple sound-vibrations correspond to sensations of simple tones, and that we can even distinguish the separate tones in compounds, can be explained, on the basis of the physical laws of sympathetic vibration, from the structure of the organs in the cochlea. The basilar membrane in the cochlea is in its different parts tuned to tones of different pitch, so that when a simple oscillatory sound-vibration strikes the ear, only the part tuned to that particular pitch will vibrate in sympathy. If the same rate of oscillation comes in a compound sound-vibration, again only the part tuned to it will be affected by it, while the other components of the wave will set in vibration other sections of the membrane, which correspond in the same way to their pitch.

11.  The system of tonal sensations shows its character as a continuous series in the fact that it is always possible to pass from a given pitch to any other through continuous changes in sensation. Music has selected at option from this continuity single sensations separated by considerable intervals, thus substituting a tonal scale for the tonal line. This selection, however, is based on the relations of tonal sensations themselves. We shall return to the discussion of these relations later, in taking up the ideational compounds arising from these sensations (§ 9). The natural tonal line has two extremities, which are conditioned by the physiological capacity of the ear for receiving sounds. These extremities are the lowest and highest tones; the former corresponds to 8-10 double vibrations per second, the latter to 40,000-50,000. [p.52]


12. Sensations of smell form a complex system whose arrangement is still unknown. All we know is that there is a very great number of olfactory qualities, between which there are all possible transitional forms. There can, then, be no doubt that the system is a continuity of many dimensions.

12a. Olfactory qualities may be grouped in certain classes, each of which contains classes sensations which are more or less related. This fact may be regarded as an indication of how these sensations may perhaps be reduced to a small number of principal qualities. Such classes are for examples, sensations like those from ether, balsam, musk, benzine, those known as aromatic, etc.

It has been observed in a few cases that certain olfactory sensations which come from definite substances, can also be produced by mixing others. But these observations are still insufficient to reduce the great number of simple, qualities contained in each of the classes mentioned, to a limited number of primary qualities and their mixtures. Finally, it has been observed that many odors neutralize each other, so far as the sensation is concerned, when they are mixed in the proper intensities. This is true not only of substances that neutralize each other chemically, as acetic acid and ammonia, but also of others, such as caoutchoue and wax or tolu-balsam, which do not act on each other chemically outside of the olfactory cells. Since this neutralization takes place when the two stimuli act on entirely differerent olfactory surfaces, one on the right and the other on the left mucous membrane of the nose, it is probable that we are dealing, not with phenomena analogous to those exhibited by complementary colors (22), but with a reciprocal central inhibition of sensations. Another observed fact tells against the notion that they are complementary. One and the same olfactory quality can neutralize several entirely different qualities, sometimes even those which in turn neutralize one another, while among colors it is always only two fixed qualities that are complementary. [p. 53]

13. Sensations of taste have been somewhat more thoroughly investigated, and we can here distinguish four, distinct primary qualities. Between these there, are all possible transitional tastes, which are to be regarded is mixed sensations. The primary qualities are sour, sweet, bitter, and saline. Besides these, alkaline and metallic are sometimes regarded as independent qualities. But alkaline qualities show an unmistakeable relationship with saline, and metallic with sour, so that both are probably mixed sensations, (alkaline made up perhaps of saline and sweet, metallic of sour and saline). Sweet and saline are opposite qualities. When these two sensations are united in proper intensifies, the result is a mixed sensation (commonly known as "insipid"), even though the stimuli that here reciprocally neutalize each other do not enter into a chemical combination. The system of taste-sensations is, accordingly, in all probability to be regarded as a two-dimensional continuity, which may be geometrically represented by a circular surface on whose circumference, the four primary, and their intermediate, qualities are arranged, while the neutral mixed sensation is in the middle, and the other transitional taste-qualities on the surface, between this middle point and the saturated qualities on the circumference.

13a. In these attributes of taste-qualities we seem to have the fundamental type of a chemical sense. In this respect taste is perhaps the antecedent of sight. The obvious interconnection with the chemical nature of the stimulation, makes it probable even here that the reciprocal neutralization of certain sensations, with which the two-dimensional character of the sensational system is perhaps connected, depends, not on the sensations in themselves, but on the relations between the physiological stimulations, just as in the case of sensations of hot and cold (p. 48). It is well known that very commonly the chemical effect of certain substances can be neutralized through the action of certain other substances. Now, we do not know what the chemical [p. 54] changes are that are produced by the gustatory stimuli in the taste-cells. But from the neutralization of sensations of sweet and saline we way conclude, in accordance with the principle of the parallelism of changes in sensation and in stimuli (p. 45), that the chemical reactions which sweet and saline substances produce in the sensory cells, also counteract each other. The same would hold for their sensations for which similar relations could be demonstrated. In regard to the physiological conditions for gustatory stimulations, we can draw only this one conclusion from the facts mentioned, namely, that the chemical processes of stimulation corresponding to the sensations which neutralize each other in this way, probably take place in the same cells. Of course, the possibility is not excluded that several different processes liable to neutralization through opposite reactions, could arise in the same cells. The known anatomical facts and the experiments of physiology in stimulating single papillae separately, give lie certain conclusions in this matter. Whether we are here dealing with phenomena that are really analogous to those exhibited by complementary colors (v. inf. 22) is still a question.


14. The system of light-sensations is made up of two partial systems: that of sensation of achromatic light and that of sensations of chromatic light. Between the qualities in these two, all possible transitional forms exist.

Sensations of achromatic light, when considered alone, form a complex system of one dimension, which extends, like the tonal line, between two limiting qualities. The sensations in the neighborhood of one of these limits we call black; in the neighborhood of the other white, while between the two we insert grey in its different shades (dark grey, grey, and light grey). This one-dimensional system of achromatic sensations differs from that of tones in being at once a system of quality and of intensity for every qualitative change in the direction from black to white is seen at the [p. 55] same time as an increase in intensity, an every qualitative change in the direction from white to black is seen as a decrease intensity. Each point in the series, which thus has a definite quality and intensity, is called a degree of brightness of the achromatic sensations. The whole system may, accordingly, be designated as the sensations of pure brightness. The use of the word "pure" indicates the absence of all sensations of color. The system of pure brightness is absolutely one-dimensional for, both the variations in quality and those in intensity belong to one and the same dimension. It differs essentially, in this respect, from the tonal line, in which each point is merely a degree of quality, and has also a whole series of gradations in intensity. Simple tone-sensations thus form a two-dimensional continuity so soon as we take into account both determinants, quality and intensity, while the system of pure brightness is always one-dimensional, even when we attend to both determinants. The whole system may, therefore, be regarded as a continuous series of grades of brightness, in which the lower grades are designated black so far as quality is concerned, and weak in point of intensity, while the higher grades are called white and strong.

15. Sensations of color also form a one-dimensional system when their qualities alone are taken into account. Unlike the system of sensations of pure brightness, this system returns upon itself from whatever point we start, for at first, after leaving a given quality, we pass gradually to a quality that shows the greatest difference, and going still further we find that the qualitative differences become smaller again, until finally we reach the starting point once more. The color-spectrum obtained by refracting sunlight through a prism, or that seen in the rainbow, shows this characteristic, though not completely. If in these cases we start from the red end of the spectrum, we come first to orange, then to yellow, yellow- [p. 56] green, green-blue, blue, indigo-blue, and finally to violet which is more like red than any of the other colors except orange, which lies next to red. The line of colors in the spectrum does not return quite to its starting-point, because it does not contain all of colors that we have in sensation. Purple-red shades, which can be obtained by the objective mixture of red and violet rays, are wanting in the spectrum. Only when we fill out the spectral series with them, is the system of actual color-sensations complete, and then the system is a closed circle. This characteristic is not to be attributed to the circumstance that the spectrum actually presents for our observation a series returning nearly to its beginning. The same order of sensations can be found by arranging according to their subjective relationship, colored objects presented in any irregular order. Even children who have never observed attentively a solar spectrum or a rainbow, and can, therefore, begin the series with any other color just as well as with red, always arrange them in the same order.

The system of pure colors is, then, to be defined as one-dimensional. It does not extend in a straight line, however, but returns upon itself. Its simplest geometrical representation would be a circle. From a given point in this system we pass, when the sensation is gradually varied, first to sensations, then to those most markedly different, and finally to others similar to the first quality, but in the opposite direction. Every color must, accordingly, be related to one other particular color as a maximum of difference in sensation. This color may be called the opposite color, and in the representation of the color-system by a circle, two opposite colors are to be placed at the two extremities of the same diameter. Thus, for example, purple-red and green, yellow and blue, light green and violet, are opposite colors, that is, colors which exhibit the greatest qualitative differences. [p. 57]

The quality determined by the position of a sensation in the color-system, in distinction to other qualitative determinations, is called color-tone, a figurative name borrowed from tonal sensations. In this sense the simple names of colors; such as red, orange, yellow, etc., denote merely color tones. The color-circle is a representation of the system of color-tones abstracted from all the other attributes belonging to the sensations. In reality, every color-sensation has two other attributes, one we call its saturation, the other its brightness. Saturation is peculiar to chromatic sensations, while brightness belongs to achromatic sensations as well.

16. By saturation we mean the attribute of color-sensations by virtue of which they appear in all possible stages of transition to sensations of pure brightness, so that a continuous passage is possible from every color to any point in the series of whites, greys, and blacks. The term "saturation" is borrowed from the common method of producing these transitional colors objectively, that is, by the more or less intense saturation of some colorless soluble with color-pigment. A color may be ever so saturated, yet it is possible to think of a still greater saturation of the same color-tone, and, on the other hand, pure brightness always denotes the end of the series of diminishing grades of saturation for any color whatever. A degree of saturation may, therefore, be thought of as an attribute of all color-sensations, and, at the same time, as the attribute by which the system of color-sensations is directly united with that of sensations of pure brightness. If, now, we represent some particular sensation of white, grey, or black by the central point of the color-circle, all the grades of saturation that can arise as transitional stages from any particular color to this particular sensation of pure brightness, will obviously be represented by that radius of the circle which connects the centre with [p. 58] the color in question. If the shades of saturation corresponding to the continuous transitional stage, from all the colors to a particular sensation of pure brightness are thus geometrically represented, we have the system of saturation-grades as a circular surface whose circumference is a system of simple color-tones, and whose centre is the sensation of pure brightness, corresponding to the absence of all saturation. For the formation of such a system of saturation-grades any point whatever in the series of sensations of pure brightness may be taken, so long as the condition is fulfilled that white is not too bright or the black too dark, for in such differences in both saturation and color disappear. Systems of saturation which are arranged about different points in the series of pure brightness, always have different grades of brightness. A pure system of saturation, accordingly, call be made for only one particular grade of brightness at a time, that is, for only one point in the series of sensations of pure brightness. When such systems are made for all possible points, the system of saturation will be supplemented by that of grades of brightness.

17. Brightness is just as an attribute of color-sensation as it is of achromatic sensations, and is in this case, too, at once a quality and degree of intensity. Starting from a given grade, if the brightness increases, every color approaches white, in quality, while at the same time the intensity increases; if the brightness decreases, the colors approach black in quality, and the intensity diminishes. The grades of brightness for any single color thus form a system of intensive qualities, analogous to that of pure brightness, only in place of the achromatic gradations between white and black, we have the corresponding grades of saturation. From the point of greatest saturation there are two opposite for variation in saturation: one positive, towards [p. 59] white, accompanied by an increase in the intensity of the sensation, and the other negative, towards black, with a corresponding decrease in intensity. As limits for these two directions we have, on the one hand, the pure sensation white, on the other, the pure sensation black; the first is at the same time the maximum, the second the minimum of intensity. White and black are in this way opposite extremities of the system of sensations of pure brightness, and also of the system of color-sensations arranged according to grades of brightness. It follows obviously that there is a certain medium brightness for every color, at which its saturation is greatest. From this point, the saturation diminishes in the positive direction when the brightness increases, and in the negative direction when the brightness decreases. The grade of brightness most favorable for the saturation is not the same for all colors, but varies from red to blue, in such a way that it is most intense for red and least intense for blue. This accounts for the familiar phenomenon that in twilight, when the degree of brightness is small, the blue color-tones -- of paintings, for example -- are still clearly visible, while the red color-tones appear black.

18.  If we neglect the somewhat different position of the maximal saturation of the various colors in the line of brightness, the relation that exists between sensations of chromatic brightness and those of pure, or achromatic, brightness, by virtue of the gradual transition of colors into white on the one hand, and into black on the other, may be represented in the simplest manner as follows. First, we may represent the system of pure color-tones, that is, of the colors at their maximal saturation, by a circle, as above. Then we may draw through the centre of this circle, perpendicular to its plane, the straight line of pure brightness, in such a way that where it cuts the plane of the circular surface, [p. 59] it represents the sensation of pure brightness corresponding to the minimum of saturation for the colors with which we started. In like manner, the other color-circles for increasing and decreasing grades of brightness, may be arranged perpendicularly along this line, above and below the circle of greatest saturation. But the decreasing saturation of the colors in these latter circles must be expressed in the shortening of their radii; just as in the first circle, the shorter the distance from the centre, the less the saturation. These radii grow continually shorter, until finally, at the two extremities of the line, the circles disappear entirely. This corresponds to the fact that for every color the maximum of brightness corresponds to the sensation white, while its minimum corresponds to black [2]

19. The whole system of sensations of chromatic brightness may, accordingly, be most simply represented by a spherical surface whose equator represents the system of pure color-tones, or colors of greatest saturation, while the two poles correspond to white and black, the extremities of the sensations of chromatic brightness. Of course, any other geometrical figure with similar attributes, as, for example, two cones with a common base and apexes pointing in different directions, would serve the same purpose. The only thing essential for the representation, is the gradual transition to white and black, and the corresponding decrease in the variety of the color-tones, which finds its expression in the continual decrease in the length of the radii of the color-circles. Now, as above shown, the system of saturations corresponding to [p. 61] a particular sensation of pure brightness, may be represented by a circular surface which contains all the sensations of light belonging to one grade of brightness. When we unite grades of saturation and brightness to a single system, the total system of light sensations may be represented by a solid sphere. The equator is the system of pure color-tones; the polar axis is the system of pure brightnesses; the surface represents the system of chromatic brightnesses, and, finally, every circular plane perpendicular to the polar axis, corresponds to a system of saturations of equal brightness. This representation by means of a sphere is indeed arbitrary, in the sense that any other solid figure with analogous attributes may be chosen in its place; still, it presents to view the psychological fact that the total system of light sensations is a closed continuity of three dimensions. The three-dimensional character of the system arises from the fact that every concrete sensation of light has three determinants: color-tone, saturation, and brightness. Pure, or achromatic, brightness and pure, or saturated, colors are to be regarded as the two extreme cases in the series of saturations. The closed form of the system comes from the circular character of the color-line, on the one hand, and, on the other, from the termination of the system of chromatic brightness in the extremes of pure brightness. A special characteristic of the system is that only the changes in the two dimensions, or those of color-tones and saturations, are pure variations in quality, while every movement in the third dimension, or that of brightness, is at once a modification of both quality and intensity. As a consequence of this circumstance, the whole three-dimensional system is required to represent the qualities of light-sensations, but it includes also the intensities of these sensations.

20. Certain principal senses are prominent in this [p. 62] system, because we use them as points of reference for the arrangement of all the others. These are, white and black, in the achromatic series, and the four principal colors, red, yellow, green, and blue, in the chromatic. Only these six sensations have clearly distinguished names in the early development of language. All other sensations are then named eiher with reference to these or with modifications of the names themselves. Thus, we regard grey as a stage in the achromatic series lying between white and black, We designate the different grades of saturation according to their brightness, as whitish or blackish, light or dark color-tones; an we generally choose compound names for the colors between the four principal ones, as, for example, purple-red, orange-yellow, yellow-green, etc. These all show their relatively late origin by their ver composition.

20a. From the early origin of the names for the six qualities mentioned, the conclusion has been drawn that they are fundamental qualities of vision, and that the others are compounded from them. Grey is declared to be a mixture of black and white, violet and purple-red to be mixtures of blue and red, etc. Psychologically there is no justification for calling any light-sensations compound in comparison with others. Grey is a simple sensation just as much as white or black; such colors as orange and purple-red are just as much simple colors as red and yellow; and any grade of saturation which we have placed in the system between a pure color and white, is by no means, for that reason, a compound sensation. The closed, continuous character of the system makes it necessary for language to pick out certain especially marked differences in reference to which all other sensations are then arranged, for the simple reason that it is impossible to have an unlimited number of names. It is most natural that white and black should be chosen as such points of reference for the achromatic series, since they designate the greatest differences. When once these two are given, however, all other achromatic sensations will be considered as transitional [p. 63] sensations between them, since the extreme differences are connected by a series of all possible grades of brightness. The case of color-sensations is similar; only here, on account of the circular form of the color-line, it is impossible to choose directly two absolutely greatest differences. Other motives besides the necessary qualitative difference, are decisive in the choice of the principal colors. We may regard as such motives, the frequency and affective intensity of certain light-impressions due to the natural conditions of human existence. The red color of blood, the green of vegetation, the blue of the sky, and the yellow of the heavenly bodies in contrast with the blue of the sky, and the yellow heavenly bodies may well have furnished the earliest occasions for the choice of certain colors as those to receive names. Language generally names the sensation from the object that produced it, not the object from the sensation. In this case too, when certain principal qualities were once determined, all others must, on account of the continuity of the series of sensations, seem to be intermediate color-tones. The difference between principal colors and transitional colors is, therefore, very probably due entirely to external conditions. If these conditions had been other, red might have been regarded as a transitional color between purple and orange, just as orange is now placed between red and yellows [3]

21. The attributes of the system of light-sensations above described, are so peculiar as to lead us to expect a priori that the relation between these psychological attributes and the objective processes of stimulation, is essentially different from that in the cases of the sensational systems discussed before, especially those of the general and auditory senses. Most [p. 64] striking, in this respect, is the difference between the system in question and that of tones. In the latter case, the principle of parallelism between sensation and stimulus (p. 45), holds not only for the physiological processes of. stimulation, but to a great extent for the physical processes as well. A simple sensation corresponds to a simple form of sound-vibration, and a plurality of simple sensations to compound form. Furthermore, the intensity of the sensation varies in proportion to the amplitude of the vibrations, and its quality with their form, so that in both directions the subjective difference between sensations increases with the growing difference between the objective physical stimuli. The relation in the case of light-sensations is entirely different. Like objective sound, objective light also consists of vibrations in some medium. To be sure, the actual form of these vibrations is still a question, but from physical experiments on the phenomena of interference we know that the consist of very short and rapid waves. Those seen as light vary in wave-length from 688 to 393 millionths of a millimetre, and in rate from 450 to 790 billion vibrations per second. In this case, too, simple sensations correspond to simple vibrations, that is, vibrations of like wave-length; and the quality of the sensation varies continuously with the rate: red corresponds to the longest and slowest wives, and violet to the shortest and most rapid, while the other color-tones form a continuous series between these, varying with the changes in wave-length. Even here, however, an essential difference appears, for the colors red and violet, which are the most different in wave-length, are more similar in sensation than those which lie between [4]

There are also other differences. 1) Every change in the amplitude of the physical vibrations corresponds to a subjective change in both intensity and quality, as we noted above in the discussion of sensations of brightness. 2) All light, even though it be made up of all the different kinds of vibration, is simple in sensation, just as much as objectively simple light, which is made up of only one kind of waves, as is immediately apparent if we make a subjective comparison of sensations of chromatic light with those of achromatic light. From the first of these facts it follows that light which is physically simple may produce not only chromatic, but also achromatic sensations, for it approaches white when the amplitude of its vibrations increases, and black when the amplitude decreases. The quality of an achromatic sensation does not, therefore, determine unequivocally its source; it may be produced either through a change in the amplitude of objective light-vibrations or through a mixture of simple vibrations of different wave-lengths. In the first case, however, there is always connected with the change in amplitude a change in the grade of brightness, which does not necessarily take place when a mixture is made.

22. Even when the grade of brightness remains constant, this achromatic sensation may have one of several sources. A sensation of pure brightness of a given intensity may result not only from a mixture of all the rates of vibration contained in solar light, as, for example, in ordinary daylight, but it may also result when only two kinds of light-waves, namely those which correspond to sensations sub- [p. 66] jectively the most different, that is, to opposite colors, are mixed in proper proportions. Since opposite colors, when mixed objectively, produce white, they are called complementary colors. As examples of such opposite or complementary colors we may mention spectral red and green-blue, orange and sky-blue, yellow and indigo-blue.

Like achromatic sensations, each of the color-sensations may also, though to a more limited extent, have one of several sources. When two objective colors which lie nearer each other in the color-circle than opposites, are mixed, the mixture appears, not white, but of a color which in the series of objectively simple qualities lies between the two with which we started. The saturation of the resulting color is, indeed, very much diminished when the components of the mixture approach opposite colors; but when they are near each other, the diminution is no longer perceptible, and the mixture and the corresponding simple color are generally subjectively alike. Thus, the orange of the spectrum is absolutely indistinguishable from a mixture of red and yellow rays. In this way, ,all the colors in the color-circle between red and green can be obtained by mixing red and green, all between green and violet by mixing green and violet, and, finally, purple, which is not in the solar spectrum, can be produced by mixing red and violet. The whole series of color-tones possible in sensation can, accordingly, be obtained from three objective colors. By means of the same three colors we can also produce white with its intermediate stages. The mixture of red and violet gives purple, and this is the complementary color of green; and the white secured by mixing these complementary colors, when mixed in different proportions with the various colors, gives the different grades of saturation.

23. The three objective colors that may be used in this way to produce the whole system of light-sensations, are [p. 67] called fundamental colors. In order to indicate their significance, a triangular surface is chosen to represent the system of saturation, rather than the circular surface which is derived from the psychological relations alone. The special significance of the fundamental colors is then expressed by placing then at the angles of the triangle. Along the sides are arranged the color-tones in their maximal saturation, just as on the circumference of the color-circle, while the other grades of saturation in their transitions to white, which lies in the centre, are on the triangular surface. Theoretically, any set of three colors could be chosen as fundamental colors, provided they were suitably distant from one another. Practically, those mentioned, red, green, and violet, are preferable for two reasons. First, by using them we avoid having as one of the three, purple, which can not be produced by objectively simple light. Secondly, at the two ends of the spectrum sensations vary most slowly in proportion to the period of vibration, so that when the extreme colors of the spectrum are used as fundamental colors, the result obtained by mixing two neighboring ones is most like the intermediate, objectively simple color. [5]

24. These phenomena show that in the system of light sensations a simple relation does not exist between the physical stimuli and the sensations. This can be understood from what has been said above (3) as to the, character of the physiological stimulation. The visual sense is to be [p. 68] reckoned among the chemical senses, and we can expect a simple relation only between the photochemical processes ill the retina and the sensations. Now, we know from experience that different kinds of physical light produce like chemical disintegrations, and this explains in general the possibility mentioned above, of having the same sensation from many different kinds of objective light. According to the principle of parallelism between changes in sensation and in the physiological stimulation (p. 45), it may be assumed that the various physical stimuli which cause the same sensation all produce the same photochemical stimulation in the retina, and that altogether there are just as many kinds and varieties of the photochemical processes as kinds and varieties of distinguishable sensations. In fact, all that we know, up to the present time, about the physiological substratum of light-sensations is based upon this assumption. The investigation of the physiological processes of stimulation through light, has not yet given any further result than that the stimulation is in all probability a chemical process.

25. The relatively long persistence of the sensation after the stimulation that originated it, is explicable on the assumption that the light-stimulations are due to chemical processes in the retina (3, p. 42). This persistence is called, with reference to the object used as stimulus, the after-image of the impression. At first this after-image appears in the same brightness and color as the object: white when the object is white, black when it is black, and if it is colored, in the same color. These are the positive and like-colored after-images. After a short time it passes, in the case of achromatic impressions, into the opposite grade of brightness, white into black, or black into white; in the case of colors, it passes into the opposite or complementary color. These are the negative and complementary after-images. If light-stimuli of short duration [p. 69] act upon the eye in darkness, this transition may be repeated several times. A second positive after-image follows the negative, and so on, so that an oscillation between the two phases takes place. The positive after-image may be readily explained by the fact that the photochemical disintegration caused by any kind of light, lists a short time after the action of the light. The negative and complementary after-images can be explained by the fact that disintegration in a given direction causes a partial consumption of the photochemical substance most directly concerned, and this results in a corresponding modification of the photochemical processes when the stimulation of the retina continues.

26. The origin of a part of the phenomena included under the name light contrasts and color-contrasts is very probably the same as that of the negative and complementary after-images. These phenomena consist in the appearance of simultaneous sensations of opposite brightness and color in the neighborhood of any light-impression. Thus, a white surface appears to be surrounded by a dark margin, a black surface by a bright margin, and a colored surface by a margin of the complementary color. These phenomena, which are called "marginal contrasts" when they are limited to the immediate neighborhood of the object, are in part at least nothing but negative or complementary after-images that are simultaneously visible in the immediate neighborhood of the impression as a result of continual weak ocular movements. Whether there is also an irradiation of the stimulation is a question; its existence still wants certain proof. The fact that these contrasts increase as the light becomes more intense, just as after-images do, speaks for their interconnection with the latter. In this respect, this physioloical contrast differs essentially from certain psychological contrast-phenomena, with which it is generally confused. The latter are closely connected in [p. 70] their rise, with numerous other forms of psychological contrast, so that we will not discuss them until later, when we enter into the general treatment (§17, 9) of such phenomena.

26a. If we take the priciple of parallelism between sensation and physiological stimulation as the basis of our suppositions in regard to the processes that occur in the retina, we may conclude that analogous independence in the photochemical processes corresponds to the relative independence which appears between achromatic and chromatic sensations. Two facts, one belonging to the subjective sensational system, the other to the objective phenomena of color-sensation can be most naturally explained on this basis. The first is the, tendency that every color-sensation shows, of passing into one of pure brightness when the grade of its brightness decreases or increases. This tendency is most simply interpreted on the assumption that every color-stimulation is made up of two physiological components, one corresponding to the chromatic, the other to the achromatic stimulation. To this assumption we may easily add the further condition, that for certain medium intensifies of the stimuli the chromatic components are the strongest, while for greater and smaller intensifies the achromatic components come more and more to the front. The second fact, is that any two opposite colors are complementary; that is, when mixed in suitable proportions, they produce an achromatic sensation. This phenomenon is most easily understood when we assume that opposite colors, which are subjectively the greatest possible differences, represent objective photochemical processes that neutralize each other. The fact that as a result of this neutralization an achromatic stimulation arises, is very readily explained by the presupposition that such a stimulation accompanies every chromatic stimulation from the first, and is therefore all that is left when antagonistic chromatic stimulations counteract each other. This assumption of a relative independence between the chromatic and achromatic photochemical processes, is supported in a very striking way by the existence of an abnormity of vision, sometimes congenital, sometimes acquired through pathological changes in the retina, namely total color-blindness. In such cases all stimulations are, either on the whole [p. 71] retina or on certain parts of it, seen as pure brightness, without any admixture of color. This is an incontrovertible proof that the chromatic and achromatic stimulations are separable physiological processes.

If we apply the principle of parallelism to the chromatic stimulation, two facts present themselves. The first is that two colors separated by limited, short distance, when mixed give a color that is like the intermediate simple color. This indicates that color-stimulation is a process that varies with the physical stimulus, not continuously, as the tonal stimulation, but in short stages, and in such a way that the stages in red and violet are longer than in green, where the mixture of colors fairly near each other, shows the effects of complementary action. Such a non-continuous variation of the process corresponds entirely with its chemical nature, for chemical disintegration and synthesis must always have to do with qroups of atoms or molecules. The second fact is that certain definite colors, which correspond to rather large differences in the stimuli, are subjectively opposite colors, that is, are maximal differences, and the same colors are objectively complementary, that is, mutually neutralizing, processes. Chemical processes, however, can neutralize each other only when they are in some way opposite in character. Any two complementary color-stimulations must, therefore, stand in a relation to each other similar to that which exists between the neutralizing processes operative in the case of antagonistic achromatic stimulations. Still, there are two very essential differences here. First, this opposition in the character of color-stimulations is not limited to one case, but appears for every color distinguishable in sensation, so that we must conclude, according to our presupposition, that for every stage of the photochemical process of. chromatic stimulation which is to be assumed on the ground of the results obtained by mixing neighboring colors, there is a certain complementary process. Secondly, the difference between two opposite colors, which is subjectively the greatest possible difference, is mediated by transitional forms, not merely in one direction from each color, as in the case of black and white, but in two opposite directions. In a similar way, the objective complementary action of two colors gradually diminishes as, starting from opposite colors, they approach each other in either of [p. 72] these two directions. We may, then, infer from this twofold elimination of complementary action that the return of the color-line to its starting point corresponds to a repetition of related photochemical processes, on the same grounds that led us to infer the opposite character of the processes corresponding to opposite colors, from the fact that they are complementary. The whole process of chromatic stimulation, beginning with red and passing beyond violet through purple mixtures to its starting point, running parallel, as it does., with continuous changes in the wavelength of objective light, is to be regarded as an indefinitely long succession of photochemical processes. All these processes together, form a closed circle in which, for every stage there is a neutralizing opposite and a possible transition to this opposite in two different directions.

We know nothing about the total number of photochemical stages in this circle of processes. The numerous attempts made to reduce all color-sensations to the smallest possible number of such stages, lack adequate foundation. Sometimes they indiscriminately translate the results of physical color-mixing into physiological processes, as in the assumption of three fundamental colors, red, green, and violet, from the different mixtures of which all sensations of light, even the achromatic, are to be derived (Young-Helmholtz hypothesis). Sometimes they start with the psychologically untenable assumption that the naming of colors is not due to the influence of certain external objects, but to the real significance of the corresponding sensations (v. sup. p. 63), and assume accordingly four fundamental colors as the sources of all color-sensations. The four fundamental colors here assumed are the two pairs red and green, yellow and blue, to which are added the similar pair of sensations of pure brightness, black and white. All other light-sensations such as grey, orange, violet, etc., are regarded as subjectively and objectively mixed colors (Hering's hypothesis). The evidence in support of the first as of the second of these hypotheses has been derived for the most part from the riot infrequent cases of partial color-blindness. Those who accept three fundamental colors, assert that all these cases are to be explained as a lack of the red or green sensations, or else as a lack of both. Those who accept four, hold that partial color-blindness always includes two fundamental colors that belong together as opposites, and is, therefore, either [p. 73] red-green-blindness or yellow-blue-blindness. An unprejudiced examination of color-blindness does not justify either of these assertions. The three-color theory can not explain total color blindness, and the four-color theory is in contradiction to cases of pure red-blindness and pure green-blindness. Finally, both theories are overthrown by the cases that unquestionably occur, in which such parts of the spectrum as do not correspond to any of the three or four fundamental colors, appear colorless. The only thing that our present knowledge justifies us in saying, is that every simple sensation of light is conditioned physiologically by a combination of two photochemical processes, a monochromatic and a chromatic. The first is made up, in turn, of a process mainly of disintegration, when the light is more intense, and a process of restitution, when the light is weaker. The chromatic process varies by stages in such a way that the whole series of photochemical color-disintegrations forms a circle of processes in which the products of the disintegration for any two relatively most distant stages, neutralize each other. [6]

Various changes as a result of the action of light have been observed in the living retina, all of which go to support the assumption of a photochemical process. Such are the gradual change into a colorless state, of a substance which in the retina not exposed to light is red (bleaching of the visual purple); microscopical movements of the pigmented protoplasm between the sensitive elements, or rods and cones; and, finally, changes in the form of the rods and cones themselves. Attempts to use these phenomena in any way for a physiological theory of light stimulation, are certainly premature. The most probable conclusion which we can now draw is that the difference in the [p. 74] forms of the rods and cones is connected with a difference in function. The centre of the retina, which is the region of direct vision in the human eye, has only cones, while in the eccentric parts the rods are more numerous; furthermore, in the centre (which also wants the visual purple) the discrimination of colors is much better than in the eccentric regions, while the latter are much more sensitive to brightness. The natural conclusion from these facts is that the differences in sensitivity are connected with the photochemical properties of the rods and cones. Still, we lack here too any particular evidence.

[1] Pendulum-oscillations may be represented by a sine-curve, because the distance from the position of rest is always proportional to the sine of the time required to swing to the point in question.

[2] It must be observed, however, that the actual coincidence of these sensations can be empirically proved only for the minimum of brightness. Grades of brightness which approach the maximum are so injurious to the eye that the general demonstration of the approach to white must be accepted as sufficient.

[3] The same false reasoning from the names of sensations, has even led some scholars to assume that the sensation blue developed later than other color-sensations, because, for example, even in Homer the word for blue is the same as that for "dark". Tests of the color-sensations of uncivilized peoples whose languages are much more deficient in names for colors than that of the Greeks at the time of Homer, have given us a superabundance of evidence that this assumption is utterly without ground.

[4] Many physicists, to be sure, believe that an analogous relation is to be found between tones of different pitch, in the fact that every tone has in its octave a similar tone. But this similarity, as we shall see (§ 9), does not exist between simple tones, but depends on the actual sympathetic vibration of the octave in all compound clangs. Attempts to support this supposed analogy by finding in the color-line intervals corresponding to the various tonal intervals, third, fourth, fifth, etc., have all been entirely futile.

[5] In the neighborhood of green this advantage does not exist, and the mixtures always appear less saturated than the intermediate simple colors. This is a clear proof that the choice of the three fundamental colors mentioned is indeed the most practical, but nevertheless arbitrary, and at bottom due to the familiar geometrical principle that a triangle is the simplest figure that can enclose a finite number of points in the same plane.

[6] The further assumption is made by the defenders of the four fundamental colors, that two opposite colors are related just as bright and dark achromatic stimulations, that is, that one of these colors is due to a photochemical disintegration (dissimilation), the other to a restitution (assimilation). This is an analogy that contradicts the actual facts. The result obtained by mixing complementary colors is on its subjective side a suppression of the color-sensation, while the mixture of white and black, on the other band, produces an intermediate sensation.



1. Feelings, like all psychical phenomenal are never permanent states. In the psychological analysis of a composite feeling, therefore, we must always think of a momentary affective state as held constant. This is easier the more slowly and continuously the psychical processes occur, so that the word feeling has come to be used mainly for relatively slow processes and for those which in their regular form of occurence never pass beyond a certain medium intensity, such as the feelings of rhythm. Where, on the other hand, a series of feelings succeeding one another in time unite to an interconnected process which is distinguished from preceding and following processes as an individual whole, and has in general a more intense effect on the subject than a single feeling, we call the unitary succession of feelings an emotion.

This very name indicates that it is not any specific subjective contents of experience which distinguish emotion from feeling, but rather the effect which comes from a special combination of particular affective contents. In this way it comes that there is no sharp line of demarcation between feeling and emotion. Every feeling of greater intensity passes into an emotion, and the separation between the two depends on a more or less arbitrary abstraction. In the case of feelings that have a certain particular form of occurence [sic], that is feelings of rhythm, such an abstraction is strictly speaking impossible. The feeling of rhythm is distinguished at most by the small intensity of its moving effect on the subject, which is what gives "emotion" its name. Still, even this distinction is by no means fixed, and when the feelings produced by rhythmical impressions become somewhat more intense, as is usually the case, especially when the rhythm [p. 170] is connected with sensational contents that arouse the feelings greatly, they become in fact emotions. Feelings of rhythm are for this reason important aids both in music and poetry for portraying emotions and arousing them in the auditor.

The names of different emotions, like those of feelings, do not indicate single processes, but classes in which a large number of single affective processes are grouped on the ground of certain common characteristics. Emotions such as those of joy, hope, anxiety, care, and anger, are accompanied in any concrete case by peculiar ideational contents, while their affective elements also and even the way in which they occur may vary greatly from time to time. The more composite a, psychical processes is, the more variable will be its single concrete manifestations; a particular emotion, therefore, will be less apt to recur in exactly the same form than will a particular feeling. Every general name fore motions indicates, accordingly, certain typical forms in which related affective processes occur.

Not every interconnected series of affective processes is an emotion or can be classed as such under one of the typical forms discriminated by language. An emotion is a unitary whole which is distinguished from a composite feeling only through the two characteristics that it has a definite temporal course and that it exercises a more intense present and subsequent effect on the interconnection of psychical processes. The first characteristic arises from the fact that an emotion is a process of a higher order as compared with a single feeling, for it always includes a succession of several feelings. The second is closely connected with this first characteristic; it depends on the intensification of the effect produced by a summation of the feelings.

As a result of these characteristics emotions have in the [p. 171] midst of all their variations in form a regularity in the manner of their occurence. They always begin with a more or less intense inceptive feeling which is immediately characteristic in its quality and direction for the nature of the emotion, and is due either to an idea produced by an external impression (outer emotional stimulation) or to a psychical process arising from associative or apperceptive conditions (inner stimulation). After this inceptive feeling comes an ideational process accompanied by the corresponding feelings. This process shows characteristic differences in the cases of particular emotions both in the quality of the feelings and in the rapidity of the process. Finally, the emotion closes with a terminal feeling which continues even after the emotion has given place to a quiet affective state, and in which the emotion gradually fades away, unless it passes directly into the inceptive feeling of a new emotion. This last case occurs especially in feelings of the intermittent type (cf. inf. 13).

4. The intensification of the effect which may be observed in the course of an emotion, relates not merely to the psychical contents of the feelings that compose it, but to the physical concomitants as well. For single feelings these accompanying phenomena are limited to very slight changes in the innervation of the heart and respiratory organs, which can be demonstrated only by using exact graphic methods (p. 86 sq). With emotions the case is essentially different. As a result of the summation and alternation of successive affective stimuli there is here not only an intensification of the effect on heart, blood-vessels, and respiration, but the external muscles are always affected in an unmistakable manner. Movements of the oral muscles appear at first (mimetic movements), then movements of the arms and of the whole body (pantomimetic movements). In the case of [p. 172] stronger emotions there may be still more extensive disturbances of innervation, such as trembling, convulsive contractions of the diaphragm and of the facial muscles, and paralytic relaxation of the muscles.

Because of their symptomatical significance for the emotions, all these movements are called expressive movements. As a rule they are entirely involuntary, either reflexes following emotional excitations, or impulsive acts prompted by the affective components of the emotion. They may be modified, however, in the most various ways through voluntary intensification or inhibition of the movements or even through intentional production of the same, so that the whole series, of external reactions which we shall have to discuss under volitional acts, may take part in these expressive movements (§ 14). These different forms of movement may be entirely alike in external character and may pass into each other without sharp limitations on their psychical side, so that for the outside observer they are as a rule indistinguishable.

5. According to their symptomatical character, expressive movements may be divided into three classes. 1) Purely intensive symptoms; these are always expressive movements for more intense emotions, and consist of stronger movements for emotions of middle intensity, and of sudden inhibition and paralysis of movement for violent emotions. 2) Qualitative expression of feelings; these are mimetic movements, the most important of which are the reactions of the oral muscles, resembling the reflexes following sweet, sour, and bitter impressions of taste; the reaction for sweet corresponds to pleasurable emotions, those for sour and bitter to unpleasurable, while the other modifications of feeling, such as excitement and depression, strain and relief, are expressed by a tension of the muscles. 3) Expression of ideas; these are generally pantomimetic movements that either point to the [p. 173] object of the emotion (indicative gestures) or else describe the objects as well as the processes connected with them by the form of the movement (depicting gestures). Obviously these three classes of expressive movements correspond exactly to the psychical elements of emotions and their fundamental attributes: the first to their intensity, the second to the quality of the feelings, and the third to their ideational content. A concrete expressive movement may unite all three forms in itself. The third class, that of expressions of ideas, is of special psychological significance because of its genetic relations to speech (cf. § 21, 3).

6. The changes in pulse and respiration that accompany emotions are of three kinds. 1) They may consist of the immediate effects of the feelings that make up the emotions, as, for example, a lengthening of the pulse-curve and respiration-curve when the feelings are pleasurable, and a shortening of the same for unpleasurable feelings (cf. sup. p. 87). This holds only for relatively quiet emotions where the single feelings have sufficient time to develop. When this is not the case, other phenomena appear which depend not merely on the quality of the feelings, but also, and that mainly, on the intensity of the innervations due to their summation. 2) Such summations may consist of intensified innervation, which arises from an increase in the excitation resulting from a summation when the succession of feelings is not too rapid. This increase shows itself in retarded and strengthened pulse-beats, since the intense excitation effects most the inhibitory nerves of the heart. Besides these there is usually an increased innervation of the mimetic and pantometic muscles. These are called sthenic emotions. 3) If the feelings are very violent or last an unusually long time in a single direction, the emotion brings about a more or less extended paralysis of the innervation of the heart and [p. 174] of the tension of the outer muscles. Under certain circumstances disturbances in the innervation of special groups of muscles appear, especially those of the diaphragm and the sympathetic facial muscles. The first symptom of the paralysis of the regulative cardiac nerves is a marked acceleration of the pulse and a corresponding acceleration of the respiration, accompanied by a weakening of the same, and a relaxation of the tension of the external muscles to a degree equal to that in paralysis. These are the asthenic emotions. There is still another distinction, which is not important enough, however, to lead to the formation of an independent class of physical effects of emotions, since we have to do here only with modifications of the phenomena characteristic of sthenic and asthenic emotions. It is the distinction between rapid and sluggish emotions, based upon the greater or less rapidity with which the increase or inhibition of the innervation [sic] appears.

6a. Older psychology, following the method of Spinoza's famous doctrine of emotions, generally offered all kinds of logical reflections about emotions, for a theory of emotions or even for description of them. In recent times, on the other hand, the expressive movements and the other concomitants of emotion in the changes of innervation in pulse, respiratory organs, and blood-vessels, have attracted the most attention. Still, these phenomena, which are indeed valuable when rightly interpreted, are often used in a very wrong way as a means for the investigation of the psychological nature of affective processes. This has in turn led to a classification of emotions based entirely on their physical characteristics, and the strange theory has gained adherence that emotions are nothing but the results of expressive movements. The emotion of sorrow, for example, is regarded as made up entirely of the sensations that come from the mimetic of weeping. In a somewhat more moderate way the attempt has been made to use the expressive movements characteristics whose presence may be [p. 175] regarded as a mark to distinguish emotions from feelings. This is, however, unjustifiable since similar physical expressive phenomena appear even for the feelings, and the minor circumstance that these symptoms are in one case externally more or less clearly visible, evidently can not be decisive. The essential difference between emotion and feeling is psychological. The emotion is made up of a series of feelings united into a unitary whole. Expressive movements are the results, on the physical side, of the increase which the preceding parts of such a series have on those succeeding. It follows directly that the deciding characteristics for the classification of emotions must be psychological (cf. inf. 9).

7. Though important constituents of emotions, the physical concomitants stand in no constant relation to the psychical quality of the same. This holds especially for the effects on pulse and respiration, but also for the pantomimetic expressive movements of stronger emotions. It may sometimes happen that emotions with very different, even opposite kinds of affective contents, may belong to the same class so far as the accompanying physical phenomena are concerned. Thus, for example, joy and anger may be in like manner sthenic emotions. Joy accompanied by surprise may, on the contrary, present the appearance, on its physical side, of an asthenic emotion. The general phenomena of innervation which give rise to the distinction between sthenic and asthenic, and rapid and sluggish emotions, do not show the character of affective contents of these emotions, but only the formal attributes of the intensity and rapidity of the feelings. This is clearly proved by the fact that differences in involuntary innervation analogous to those which, accompany the different emotions, may be produced by a mere succession of indifferent impressions, as, for example, by the strokes of a metronome. It is observed in such a case that especially the respiration tends to adapt itself to [p. 176] the faster or slower rate of the strokes, becoming more rapid when the rapidity of the metronome increases. As a rule, too, certain phases of respiration coincide with particular strokes. To be sure, the hearing of such an indifferent rhythm is not unattended by emotion. When the rate changes, we observe at first a quiet, then a sthenic, and finally when the rapidity is greatest an asthenic emotion. Still the emotions in this case have to a certain extent a mere formal character; they exhibit a great indefiniteness in their contents. This indefiniteness disappears only when we think into them concrete emotions of like formal attributes. This is very easy, and is the condition of the great utility of rhythmical impressions for describing and producing emotions. All that is necessary to arouse an emotion in all its fulness is a mere hint of qualitative affective content, such as it is possible to give in music through the clangs of a musical composition.

7a. It follows from this relation of the physical effects to the psychical content of emotions, that the former can never be put in the place of the psychological observation of the emotions. They are general symptoms, but of such equivocal character that, though they are of great value when connected with introspection controlled by experimental methods, alone they have no value whatever. They are especially useful as cheeks for experimental introspection. The principle that the observation of psychical processes which present themselves in the natural course of life is entirely inadequate, holds especially for the emotions. In the first place, emotions come to the psychologist by chance, at moments when he is not in a condition to subject them to scientific analysis; and secondly, in the case of strong emotions whose causes are real we are least of all able to observe ourselves with exactness. This can be done much more successfully when we arouse in ourselves voluntarily a particular emotional state. In such a case, however, it is not possible to estimate how nearly the subjectively aroused emotion agrees in [p. 177] intensity and mode of occurence [sic] with one of like character due to external circumstances. For this purpose the simultaneous investigation of the physical effects, especially of those most removed from the influence of the will of those on the pulse and respiration, furnishes a check for introspection. For when the psychological quality of emotions is alike, we may infer from their like physical effects that their formal attributes also agree.

8. Both in natural and in voluntarily aroused emotions, the physical concomitants have, besides their symptomatical significance, the important psychological attribute of intensifying the emotion. This attribute is due to the fact that the excitation or inhibition of certain particular groups of muscles is accompanied by inner tactual sensations which produce certain sense-feelings. These feelings unite with the other affective contents of the emotion and increase its intensity. From the heart, respiratory organs, and blood-vessels we have such feelings only for strong emotions, where they may indeed be very intense. On the other hand, even in moderate emotions the state of greater or less tension of the muscles exercises an influence on the affective state and thereby on the emotion.

9. The great number of factors that must be taken into consideration for the investigation of emotions renders a psychological analysis of the single forms impossible. This is all the more so because each of the numerous distinguishing names marks off a whole class, within which there is a great variety of special forms, including in turn an endless number of single cases of the most various modifications. All we can do is to take a general survey of the fundamental form of emotions. The general principles of division here employed must, of course, be psychological, that is, such as are derived from the immediate attributes of the emotions themselves, for the accompanying physical phenomena have [p. 178] only a symptomatical value and are even then, as noted above, equivocal in character.

Three such psychological principles of classification may be made the basis for the discrimination of emotions: 1) according to the quality of the feelings entering into the emotions, 2) according to the intensity of these feelings, 3) according to the form of occurence, which is conditioned by the character and rate of the affective changes.

10. On the basis of quality we may distinguish certain fundamental emotional forms corresponding to the chief affective directions distinguished before (p. 83). This gives us pleasurable and unpleasurable, exciting and depressing, straining and relaxing emotions. It must be noted, however, that because of their more composite character the emotions, are always, even more than the feelings, mixed forms. Generally, only a single affective direction can be called the primary tendency for a particular emotion. There are affective elements belonging to other directions, that enter in as secondary elements. Their secondary character usually appears in the fact that under different conditions various sub-forms of the primary emotion may arise. Thus, for example, joy is primarily a pleasurable emotion. Ordinarily it is also exciting, since it intensifies the feelings, but when the feelings are too strong, it becomes a depressing emotion. Sorrow is an unpleasurable emotion, generally of a depressing character; when the intensity of the feelings becomes somewhat greater, however, it may become exciting, and when the intensity becomes maximal, it passes again into very marked depression. Anger is much more emphatically exciting and unpleasant in its predominant characteristics, but when the intensity of the feelings becomes greater, as when it develops into rage, it may become depressing. Thus, exciting and depressing tendencies are always mere secondary qualities [p. 179] connected with pleasurable and unpleasurable emotions. Feelings of strain and relaxation, on the contrary, may more frequently be the chief, or at least the primary components of emotions. Thus, in expectation, the feeling of strain peculiar to this state is the primary element of the emotion. When the feeling develops into an emotion, it may easily be associated with unpleasurable feelings which are, according to circumstances either exciting or depressing. In the case of rhythmical impressions or movements there arise from alternation of feelings of strain with those of relaxation pleasurable emotions which may be either exciting or depressing according to the character of the rhythm. When they are depressing we may even have unpleasurable feelings intermingled with them, or they may all be of this kind, especially when other affective elements cooperate, for example feelings of clang or harmony.

11. Language has paid the most attention in its development of names for emotions to the qualitative side of feelings, and among these qualities particularly to pleasurable and unpleasurable. These names may be divided into three classes. First we have those of emotions that are subjectively distinguished, chiefly through the nature of the affective state itself, such as joy and sorrow and, as subforms of sorrow in which either depressing, straining, or relaxing tendencies of the feeling are also exhibited, sadness, care, grief, and fright. Secondly, there are names of objective emotions referring to some external object, such as delight and displeasure and, as subforms of the latter in which, as above, various tendencies unite, annoyance, resentment, anger, and rage. Thirdly, we have names of objective emotions that refer rather to outer events not expected until the future, such as hope and fear and, as modifications of the latter, worry and anxiety. They are combinations of feelings of strain [p. 180] with pleasurable and unpleasurable feelings and, in different ways, with exciting and depressing tendencies as well.

Obviously language has produced a much greater variety of names for unpleasurable emotions than for pleasurable. In fact, observation renders it probable that unpleasurable emotions exhibit a greater variety of typical forms of occurence. and that their different forms are really more, numerous.

12. On the basis of the intensity of the feelings we may distinguish weak and strong emotions. These concepts, derived from the psychical properties of the feelings, do not coincide with those of sthenic and asthenic emotions, based upon the physical concomitants, for the relation of the psychological categories to the psycho-physical is dependent not only on the intensity of the feelings, but on their quality as well. Thus, weak and moderately strong pleasurable emotions are always sthenic, while, on the contrary, unplesurable emotions become asthenic after a longer duration, even when they are of a low degree of intensity, as, for example, care and anxiety. Finally, the strongest emotions, such as fright, worry, rage, and even excessive joy, are always asthenic. The discrimination of the psychical intensity of emotions is accordingly of subordinate significance, especially since emotions that agree in all other respects, may not only have different degrees of intensity at different times, but may on the same occasion vary from moment to moment. Then too since this variation from moment to moment is essentially determined by the sense-feelings that arise from the accompanying physical phenomena, in accordance with the principle of the intensification of emotions discussed above (p. 177), it is obvious that the originally physiological antithesis of sthenic and asthenic often has a more decisive influence even on the psychological character of the emotion than the primary psychical intensity itself. [p. 181]

13. The third distinguishing characteristic of emotions the form of occurence, is more important. Here we distinguish three classes. First, there are sudden, irruptive emotions, such as surprise, astonishment, disappointment, fright, and rage. They all reach their maximum very rapidly and then gradually sink to a quiet affective state. Secondly, we have gradually arising emotions, such as anxiety, doubt, care, mournfulness, expectation, and in many, cases joy, anger, worry. These rise to their maximum gradually and sink in the same way. As a third form and at the same time a modification of the class just mentioned we have intermittent emotions, in which several, periods of rise and fall follow one another alternately. All emotions of long duration belong here. Thus, especially joy, anger, mournfulness, and the most various forms of gradually arising emotions, come in waves and often permit a distinction between periods of increasing and those of decreasing emotional intensity. The sudden, irruptive emotions, on the contrary, are seldom intermittent. This happens only in cases in which the emotion may also belong to the second class. Such emotions of a very changeable form of occurence [sic] are, for example, joy and anger. They may sometimes be sudden and irruptive. In this case, to be sure, anger generally becomes rage. Or they may gradually rise and fall; they are then generally of the intermittent type. In their psycho-physical concomitants, the sudden irruptive emotions are all asthenic, those gradually arising may be either sthenic or asthenic.

13a. The form of occurence [sic], then, however characteristic it may be in single cases, is just as little a fixed criterion for the Psychological classification of emotions as is the intensity of the feelings. Obviously such a classification can be based only on the quality of the affective contents, while intensity and form of occurence may furnish the means of subdivision. The way [p. 182] in which these conditions are connected with one another and with the accompanying physical phenomena and through these with secondary sense-feelings, shows the emotions to be most highly composite psychical processes which are therefore in single cases exceedingly variable. A classification that is in any degree exhaustive must, therefore, subdivide such varying emotions as joy, anger, fear, and anxiety into their subforms, according to their modes of occurence, the intensity of their component feelings, and finally according to their physical concomitants which are dependent on both the psychical factors mentioned. Thus, for example, we may distinguish a strong, a weak, and a variable form of anger, a sudden, a gradually arising, and an intermittent form of its occurence, and finally a sthenic, asthenic, and a mixed form of its expressive movements. For the psychological explanation, an account of the causal interconnection, of the single forms in each particular case is much more important than this mere classification. In giving such an accounts we have in the case of every emotion to do with two factors, first, the quality and intensity of the component feelings, and second, the rapidity of the succession of these feelings. The first factor determines the general character of the emotion, the second its intensity in part and more especially its form of occurence, while both together determine its physical accompaniments and the psycho-physical changes resulting from the sense-feelings connected with these accompanying phenomena (p. 177). It is for this very reason that the physical concomitants are as a rule to be called psycho-physical. The expressions "psychological" and "psycho-physical" should not, however, be regarded as absolute opposites in this case, where we have to do merely with symptoms of emotion. We speak of psychological emotional phenomena when we mean those that do not show any immediately perceptible physical symptoms, even when such symptoms can be demonstrated with exact apparatus (as, for example, changes in the pulse and in respiration). On the other hand we speak of psycho-physical phenomena in the case of those which can be immediately recognized as two-sided.



1. The fact that the psychical development of man is regularly slower than that of most animals is to be seen in the much more gradual maturing of his sense-functions. The child, to be sure, reacts immediately after birth to all kinds of sense-stimuli, most clearly to impressions of touch and taste, with the least certainty to those of sound. Still, it is impossible to doubt that the special forms of the reaction-movements in all these cases are due to inherited reflexes. This is especially true for the child's crying when afected by cold and tactual impressions, and for the mimetic reflexes when he tastes sweet, sour, or bitter substances. It is probable that all these impressions are accompanied by obscure sensations and feelings, yet the character of the movements can not be explained from the feelings whose symptoms they may be considered to be, but must be referred to connate central reflex tracts.

Probably nothing is clear in consciousness until the end of the [p. 284] first month, and even then, as the rapid change of moods shows, sensations and feelings must be relatively very changeable. It is at about this time that we begin to observe symptoms of pleasurable and unpleasurable feelings in the child's laughter and in lively rhythmical movements of his arms and legs after certain impressions. Even the reflexes are not completely developed at first -- a fact which we can easily understand when we learn from anatomy that many of the connecting fibres between the cerebral centres do not develop until after birth. Thus the associative reflex-movements of the two eyes are wanting. From the first each of the eyes by itself generally turns towards a light, but the movements of the two eyes are entirely irregular, and it is only in the course of the first three months that the normal coordination of the movements of the two eyes with a common fixation-point, begins to appear. Even then the developing regularity is not to be regarded as a result of complete visual perceptions, but, quite the reverse, as a symptom of the gradual functioning of a reflex-centre, which then renders clear visual perceptions possible.

2. It is, generally speaking, impossible to gain any adequate information about the qualitative relations of psychical elements in the child's consciousness, for the reason that we have no certain objective symptoms. It is probable that the number of different tonal sensations, perhaps also the number of color-sensations, is very limited. The fact that children two years old not infrequently use the wrong names for colors ought not however, to be looked upon as unqualified evidence, that they do not have the sensation in question. It is much more probable that lack of attention and a confusion of the names is the real explanation in such cases.

Towards the end of the first year the differential of feelings and the related development of the various emotions [p. 285] take place, and show themselves strikingly in the characteristic expressive movements that gradually arise. We have unpleasurable feelings and joy, then in order, astonishment, expectation, anger, shame, envy, etc. Even in these cases the dispositions for the combined movements which express the single emotions, depend upon inherited physiological attributes of the nervous system, which generally do not begin to function until after the first few months, in a way analogous to the combined innervation of the ocular muscles. As further evidence of this we have the fact that not infrequently special peculiarities in the expressive movements are inherited by whole families.

3. The physical conditions for the rise of spacial ideas are connate in the form of inherited reflex-connections which make a relatively rapid development of these ideas possible. But for the child the spacial perceptions seem at first to be much more incomplete than they are in the case of many animals. There are manifestations of pain when the skin is stimulated, but no clear symptoms of localization. Distinct grasping movements develop gradually from the aimless movements that are observed even in the first days, but they do not, as a rule, become certain and consciously purposive until aided by visual perceptions, after the twelfth week. The turning of the eye toward a source of light as generally observed very early, is to be regarded as reflex. The same is true of the gradual coordination of ocular movements. Still it is probable that along with these reflexes there are developed spacial ideas, so that all we can observe is the gradual completion of these ideas from very crude beginnings, for the process is continuous and is always interconnected with its original physiological substratum. Even in the child the sense of sight shows itself to be decidedly more rapid in its development than the sense of touch, for the symptoms [p. 286] of visual localization are certainly observable earlier than those of tactual localization, and the grasping movements, as mentioned above, do not reach their full development until aided by the sense of sight. The field of binocular vision is much later in its development than that of monocular vision. The latter shows itself in the discrimination of directions in space. The beginnings of the development of a field for binocular vision coincide with the first coordination of ocular movements and belong, accordingly, to the second half of the first year. The perception of size, of distance, and of various three-dimensional figures remains for a long time very imperfect. Especially, distant objects are all thought to be near at hand, so that they appear relatively small to the child.

4. Temporal ideas develop along with the spacial ideas. The ability to form regular temporal ideas and the agreeableness of these to the child shows itself in the first months in the movements of his limbs and especially in the tendency to accompany rhythms that are heard, with similar rhythmical movements. Some children can imitate correctly, even before, they can speak, the rhythmical melodies that they hear, in sounds and intonations. Still, the ideas of longer intervals are very imperfect even at the end of the first year and later, so that a child gives very irregular judgements as to the duration of different periods and also as to their sequence.

5. The development of associations and of simple apperceptive combinations goes hand in hand with that of spacial and temporal ideas. Symptoms of sensible recognition (p. 237) are observable from the very first days, in the rapidly aquired ability to find the mother's breast and in the obvious habituation to the objects and persons of the environment. Still, for a long time these associations cover only very short intervals of time, at first only hours, then days. Even in [p. 287] the third and fourth years children either forget entirely or remember only imperfectly persons who bay been absent for a few weeks.

The case with attention is similar. At first it is possible to concentrate it upon a single object only for a very short time, and it is obvious that passive apperception which always follows the predominating stimulus, that is the one whose affective tone is strongest (p. 217), is the only form present. In the first weeks, however, a lasting attention begins to show itself in the way the child fixates and follows objects for a longer time, especially if they are moving; and at the same time we have the first trace of active apperception in the ability to turn voluntarily from one impression to another. From this point on, the ability becomes more and more fully developed; still, the attention, even in later childhood, fatigues more rapidly than in the case of adults, and requires a greater variety of objects or a more frequent pause for rest.

6. The development of self-consciousness keeps pace with that of the associations and apperceptions. In judging of this development we must guard against accepting as signs of self-consciousness any single symptoms, such as the child's discrimination of the parts of his body from objects of his environment, his use of the word "I", or even the recognition of his own image in the mirror. The adult savage who has never seen his own reflected image before, takes it for some other person. The use of the personal pronoun is due to the child's imitation of the examples of those about him. This imitation comes at very different times in the cases of different children, even when their intellectual development in other respects is the same. It is, to be sure, a symptom of the presence of self-consciousness, but the first beginnings of self-consciousness may have preceded this discrimination [p. 288] in speech by a longer or shorter period of time as the case may be. Again, the discrimination of the body from other objects is a symptom of exactly the same kind. The re cognition of the body is a process that regularly precedes that of the recognition of the image in the mirror, but one is as little a criterion of the beginning of self-consciousness as the other. They both presuppose the existence of some degree of self-consciousness beforehand. Just as the developed self-consciousness is based upon a number of different conditions (p. 221), so in the same way the self-consciousness of the child is from the first a product of several components, partly ideational in character, partly affective and volitional. Under the first head we have the discrimination of a constant group of ideas, under the second the development of certain interconnected processes of attention and volitional acts. The constant group of ideas does not necessarily include all parts of the body, as, for example, the legs, which are usually covered, and it may, as is more often the case, include external objects, as, for example, the clothes generally worn. The subjective affective and volitional components, and the relations that exist between these and the ideational components in external volitional acts, are the factors that exercise the decisive influence. Their greater influence is shown especially by the fact that strong feelings, especially those of pain, very often mark in an individual's memory the first moment to which the continuity of his self-consciousness reaches back. But there can be no doubt that a form of self-consciousness, even though less interconnected, exists even before this first clearly remembered moment, which generally comes in the fifth or sixth year. Still, since the objective observation of the child is not supplied at first with any certain criteria, it is impossible to determine the exact moment when self-consciousness begins. Probably the traces of it [p. 289] begin to appear in the first weeks; after this it continually becomes clearer under the constant influence of the conditions mentioned, and increases in temporal extent just as consciousness in general does.

7. The development of will is intimately connected with that of self-consciousness. It may be inferred partly from the development of attention described above, partly from the rise and gradual perfection of external volitional acts, whose influence on self-consciousness has just been mentioned. The immediate relation of attention to will appears in the fact that symptoms of active attention and voluntary action come at exactly the same time. Very many animals execute immediately after birth fairly perfect impulsive movements, that is, simple volitional acts. These are rendered possible by inherited reflex-mechanisms of a complex character. The new-born child, on the contrary, does not show any traces of such impulsive acts. Still, we observe in the first days the earliest beginnings of simple volitional acts of an impulsive character, as a result of the reflexes caused by sensations of hunger and by the sense-perceptions connected with appeasing it. These are to be seen in the evident quest after the sources of nourishment. With the obvious growth of attention come the volitional acts connected with impressions of sight and hearing: the child purposely, no longer merely in a reflex way, follows visual objects, and turns his head towards the noises that he hears. Much later come the movements of the outer muscles of the limbs and trunk. These, especially the muscles of the limbs, show from the first lively movements, generally repeated time and time again. These movements are accompanied by all possible feelings and emotions, and when the latter become differentiated, the movements begin gradually to exhibit certain differences characteristic for the quality of the emotions. The chief [p. 290] difference consists in the fact that rhythmical movement accompany pleasurable emotions, while arrhythmical and, as rule, violent movements result when the emotions are unpleasurable. These expressive movements, which must be looked upon as reflexes attended by feelings, then, as soon as the attention begins to turn upon the surroundings, pass as occasion offers into ordinary voluntary expressive movements. Thus, the child shows through the different accompanying symptoms that he not only feels pain, annoyance, anger, etc., but that the wishes to give expression to these emotions. The first movements, however, in which an antecedent motive is to be recognized beyond a doubt, are the graying movements which begin in the twelfth to the fourteenth week. Especially at first, the foot takes part in these movements as well as the hand. We have here also the first clear symptoms of sense-perception, as well as the first indications of the existence of a simple volitional process made up of motive, decision, and act. Somewhat later intentional imitative movements are to be observed. Simple mimetic imitations, such as puckering the lips and frowning, come first, and then pantomimetic, such as doubling up the fist, beating time, etc. Very gradually, as a rule not until after the beginning of the second half of the first year, complex volitional acts develop from these simple ones. The oscillation of decision, the voluntary suppression of an intended act or one already begun, commence to be clearly observable at this period.

Learning to walk, which usually begins in the last third of the first year, is an important factor in the development of voluntary acts in the proper sense of the term. Its importance is due to the fact that the going to certain particular places furnishes the occasion for the rise of a number of conflicting motives. The learning itself is to be regarded as [p. 291] a process in which the development of the will and the effect of inherited dispositions to certain particular combinations of movements are continually interacting upon each other. The first impulse for the movement comes from volitional motives; the purposive way in which it is carried out, however, is primarily an effect of the central mechanism of coordination, which in turn is rendered continually more and more purposive as a result of the individual's practice directed by his will.

8. The development of the child's ability to speak follows that of his other volitional acts. This, too, depends on the cooperation of inherited modifications in the central organ of the nervous system on one hand, and outside influences on the other. The most important outside influences in this case are those that come from the speech of those about the child. In this respect the development of speech corresponds entirely to that of the other expressive movements, among which it is, from its general psycho-physical character, to be classed. The earliest articulations of the vocal organs appear as reflex phenomena, especially accompanying pleasurable feelings and emotions, as early as the second month. After that they increase in variety and exhibit more and more the tendency to repetition (for example, ba-ba-ba, da-da-da, etc.). These expressive sounds differ from those of many animals only in their greater and continually changing variety. They are produced on all possible occasions and without any intention of communicating anything, so that they are by no means to be classed as elements of speech. Through the influence of those about the child these sounds generally become elements of speech after the beginning of the second year. This result is brought about chiefly by certain imitative movements. It comes, in the form of sound-sensations, from two sides. On the one hand, the child imitates adults, on the other, adults imitate the child. In fact, as a rule, it is the adults who [p. 292] begin the imitating; they repeat the involuntary articulations of the child and attach a particular meaning to them, as, for example, "pa-pa" for father, "ma-ma" for mother, etc. It is not until later, after the child has learned to use these, sounds in a particular sense though intentional immitation, that he repeats other words of the adults' language also, and even then he modifies them to fit the stock of sounds that he is able to articulate.

Gestures are important as means by which adults, more instinctively than voluntarily, help the child to understand the words they use. These are generally indicative gestures towards the objects; less frequently, ordinarily only in the case of words meaning seine activity such as strike, cut, walk, sleep, etc., they take the form of depicting gestures. The child has a natural understanding for these gestures, but not for words. Even the onomatopoetic words of child-speech (such as bow-bow for dog, etc.) never become intelligible to him until the objects have been frequently pointed out. The child is not the creator of these words, but it is rather the adult who seeks instinctively to accommodate himself in this respect also to the stage of the child's consciousness.

All this goes to show that the child's learning to speak is the result of a series of associations and apperceptions in whose formation both the child and those about to take part. Adults voluntarily designate particular ideas with certain words taken from the expressive sounds made by the child, or with onomatopoetic words made arbitrarily after the pattern of the first class. The child apperceives this combination of word and idea after it has been made intelligible to him with gestures, and associates it with his own imitative articulative movements. Following the pattern of these first apperceptions and associations the child their forms others, by imitating of his own accord more and more the words and [p. 293] verbal combinations that he accidentally hears adults using, and by making the appropriate associations with their meanings. The whole process is thus the result of a psychical interaction between the child and those about him. The sounds are at first produced by the child alone, those about him take up these sounds and make use of them for purposes of speech.

9. The final development that comes from all the simpler processes thus far discussed, is that of the complex function of apperception, that is the relating and comparing activities, and the activities of imagination and understanding made up of these (§ 17).

Apperceptive combination in its first form is exclusively the activity of imagination, that is the combination, analysis, and relating of concrete sensible ideas. Thus, individual development corroborates what has been said in general about the genetic relation of these functions (p. 266). On the basis of the continually increasing association of immediate impressions with earlier ideas, there arises in the child, as soon as his active attention is aroused, a tendency to form such combinations voluntarily. The number of memory-elements freely combining with the impression and added to it, furnish us with a measure for the fertility of the individual child's imagination. As soon as this combining activity of imagination has once begun to operate, it shows itself with an impulsive force that the child is unable to resist, for there is not as yet, as ill the case of adults, any activity of the understanding to prescribe definite intellectual ends regulating and inhibiting the free sweep of the ideas of imagination.

This unchecked relating and coupling of ideas in imagination is connected with volitional impulses aiming to find for the ideas some starting-points in immediate sense-perception, however vague these starting-points may be. This is what gives rise to the child's play-impulse. The earliest games of the [p. 294] child are those of pure imagination; while, on the contrary, those of adults (cards, chess, lotto, etc.) are almost as exclusively intellectual games. Only where aesthetical demands exert an influence are the games of adults the productions of the imagination (drama, piano-playing, etc.), but even here they are not wholly untrammeled like those of the child, but are regulated by the understanding. When the play of a child takes its natural course, it shows at different periods of its development all the intermediate stages between the game of pure imagination and that in which imagination and understanding are united. In the first years this play consists in the production of rhythmical movements of the arms and legs, then the movements are carried over to external objects as well, with preference to such objects as give rise to auditory sensations, or such as are of bright colors. In their origin these movements are obviously impulsive acts aroused by certain sensational stimuli and dependent for their purposive coordination on inherited traits of the central nervous organs. The rhythmical order of the movements and of the feelings and sound-impressions produced by them, obviously arouse pleasurable feelings, and this very soon results in the voluntary repetition of the movements. After this, during the first years, play becomes gradually a voluntary imitation of the occupations and scenes that the child sees about him. The range of imitation then widens and is no longer limited to what is seen, but includes a free reproduction of what is heard in narratives. At the same time the interconnection between ideas and acts begins to follow a more fixed plan. This is the regulative influence of the activity of understanding, which shows itself in the games of later childhood in perscribed rules. This development is often accelerated through the influence of those about the child and through artificial forms of play generally invented by adults and not always suited to the child's imagination; [p. 295] still, the development is to be recognized as natural and necessarily conditioned by the reciprocal interconnection of associative and apperceptive processes, since it agrees with the general development of the intellectual functions. The way in which the processes of imagination are gradually curtailed and the functions of understanding more and more employed, renders it probable that the curtailing is due not so much to a quantitative decrease of imagination as to an obstruction of its action through abstract thinking. When this has once set in, because of the predominating exercise of abstract thinking, the activity of imagination may itself through lack of use be interfered with. This view seems to be supported by the fact that savages usually have all through their lives an imaginative play-impulse related to that of the child.

10. From imaginative forms of thought as a starting point the functions of understanding develop very gradually in the way already described (p. 264). Aggregate ideas that are presented in sense-perception or formed by the combination, activity of imagination are divided into their conceptual components, into objects and their attributes, into objects and their activities, or into the relations of different objects to one another. The decisive symptom for the rise of the functions of understanding is therefore the formation of concepts. On the other hand, actions that can be explained from the point of view of the observer by logical reflection, are by no means proofs of the existence of such reflection on the part of the actor, for they are very often obviously derived from associations, just as in the case of animals. In the same way there may be the first beginnings of speech without abstract thinking in any proper sense, since words refer originally only to concrete sensible impressions. Still, the more perfect use of language is not possible until ideas are conceptually analyzed, related, and transferred, even [p. 296] though the processes are in each case entirely concrete and sensible. The development of the functions of understanding and that of speech accordingly go hand in hand, and the latter is an indispensable aid in retaining concepts and fixing the operations of thought.

10a. Child-psychology often suffers from the same mistake that is made in animal psychology: namely, that the observations aren't interpreted objectively, but are filled out with subjective reflections. Thus, the earliest ideational combinations, which are in reality purely associative, are regarded as acts of logical reflection, and the earliest mimetic expressive movements, as, for example, those of a new-born child due to taste-stimuli, are looked upon as reactions to feelings, while they are obviously at first nothing but connate reflexes which may, indeed, be accompanied by obscure concomitant feelings, but even these can not be demonstrated with certainty. The ordinary view as to the development of volition and of speech, labors under a like misconception. Generally there is a tendency to consider the child's language, because of its peculiarities, as a creation of his own. Closer observation, however, shows that it is created by those about him, though in doing this they use the sounds that the child himself produces, and conform as far as possible to big stage of consciousness. Thus it comes that some of the very detailed and praise-worthy accounts of the mental development of the child in modern literature can serve only as sources for finding objective facts. Because they stand on the basis of a reflective popular psychology, their psychological deductions require correction along the lines marked out above.

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Wundt, W.M. 1897 Outlines of Psychology. Translated, with the cooperation of the author, by Charles Hubbard Judd.
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Scientifican alysis

it was chiefly the psychology of the inner sense that developed the method of pure introspection

Introduction 2.4 Essentially distinct from the psychology of the inner sense is the form of psychology which defines itself as "the science of immediate experience".

Introduction 2.4b inner and outer experience are supplementary points of view

Introduction 2.10.2b As the science of the universal forms of immediate human experience and their combination in accordance with certain laws, [psychology] is the foundation of the mental sciences.

Introduction2.10.2c psychology pays equal attention to both the subjective and objective conditions which underlie not only theoretical knowledge, but practical activity as well

Introduction3.2 A sensation arises in us under the most favorable conditions for observation when it is caused by an external sense-stimulus, as, for example, a tone-sensation from an external tone-vibration... Memory-images, it is true, cannot be directly aroused through external sense impressions... There is, then, no fundamental psychical process to which experimental methods can not be applied, and therefore none in whose investigation they are not logically required.

One.6.5 it is impossible to explain the character of sensations from the character of physical and physiological stimuli. Stimuli and sensations can not be compared with one another at all; the first belong to the mediate experience of the natural sciences, the second to the immediate experience of psychology ... An interrelation between sensations and physiological stimuli must necessarily exist, however, in the sense that different kinds of stimulation always correspond to different sensations.... This principle of the parallelism of changes in sensation and in physiological stimulation is an important supplementary principle in both the psychological and physiological doctrines of sensation.

Two.13.5 expressive movements may be divided into three classes... [Class three] Expression of ideas; these are generally pantomimetic movements that either point to the object of the emotion (indicative gestures) or else describe the objects as well as the processes connected with them by the form of the movement (depicting gestures)

Other writers:
John Stuart Mill
John Watson
George Mead