One of the most striking features in the thoughts of primitive people is the peculiar manner in which concepts that appear to us alike and related are separated and rearranged. According to our views, the constituting elements of the heavens and of the weather are all inanimate objects; but to the mind of primitive man they appear to belong to the organic world. The dividing-line between man and animal is not sharply drawn. What seem to us conditions of an object—like health and sickness—are considered by him as independent realities. In short, the whole classification of experience among mankind living in different forms of society follows entirely distinct lines. I have illustrated the necessity of classification in a previous chapter, when speaking of the relation of language and cultural development (p. 143). Incidentally I have also pointed out that the principles of classification which are found in different languages do not by any means agree. The behavior of primitive man makes it perfectly clear that all these linguistic classes have never risen into consciousness, and that consequently their origin must be sought, not in rational, but in entirely unconscious, processes of the mind. They must be due to a grouping of sense-impressions and of concepts which is not in any sense of the term voluntary, but which develops from entirely different psychological causes. It is a characteristic of linguistic classifications that they never rise into consciousness; while other classifications, although the same unconscious origin prevails, often do rise into consciousness. It seems very plausible, for instance, that the fundamental religious notions, like the idea of will-power immanent in inanimate objects, or the anthropomorphic character of animals, are in their origin just as little conscious as the fundamental ideas of language. While, however, the use of language is so automatic that the opportunity never arises for the fundamental notions to emerge into consciousness, this happens very frequently in all phenomena relating to religion. These observations may be applied equally well to other groups of concepts. The primary object of these researches is the determination of the fundamental categories under which phenomena are classified by man in various stages of culture. Differences of this kind appear very clearly in the domain of certain simple sense-perceptions. For instance, it has been observed that colors are classified according to their similarities in quite distinct groups, without any accompanying difference in the ability to differentiate shades of color. What we call green and blue are often combined under some such term as “gall-like color”; or yellow and green are combined into one concept, which may be named “young-leaves color.” The importance of the fact that in thought and in speech these color-names convey the impression of quite different groups of sensations can hardly be overrated.