Wilhelm M. Wundt (1832-1920)

1858-1862 (Five volumes) Beiträge zur Theorie der Sinneswahrnehmung Stated the case for experimental psychology and reported some experiments in visual perception. But claimed that the higher mental processes (e.g. thought, language, belief) are not amenable to experimental investigation, but can only be studied through a socio- historical approach. (O'Neil, W.M. 1982 p.29)

1894 Lectures on Human and Animal Psychology. Vorlesungen über die Menschen-und Tierseele (2nd edition), translated into English by J.E. Creighton and E.B. Titchener.

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

1900 Völkerpsychologie: eine Untersuchung der Entwicklungsgesetze von Sprache, Mythus und Sitte. [Started as one volume. Became ten volumes by 1920]

1904 Principles of Physiological Psychology. Grundzüge der physiologischen Psychologie (5th edition), translated into English by E.B. Titchener.

1906 Völkerpsychologie. Vol.2, Part 2: Mythus and Religion is discussed by Freud in Totem and Taboo

1912 Elemente der Völkerpsychologie Leipzig. also discussed by Freud in Totem and Taboo. (quotes on totem)

1916 Elements of Folk Psychology Elemente der Völkerpsychologie, translated into English by E.L. Schaub.

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.

[One definition of] 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.
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Scientific analysis shows that many components of experience - as, for example, sensations - are subjective effects of objective processes
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it was chiefly the psychology of the inner sense that developed the method of pure introspection
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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
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inner and outer experience are supplementary points of view
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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. The subject-matter of these sciences is in all cases of the activities proceeding from immediate human experiences, and their effects.
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psychology pays equal attention to both the subjective and objective conditions which underlie not only theoretical knowledge, but practical activity as well
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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 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.