While these special characteristics of man are inseparable from his social life, they also stand in strong relation to each other. These characteristics have not been developed singly, but all have progressed in common. That thought and language can exist and develop only in common is known to everyone who has but tried to think of the nature of his own thoughts. When we think or consider, we, in fact, talk to ourselves; we observe then that it is impossible for us to think clearly without using words. Where we do not think with words our thoughts remain indistinct and we can not combine the various thoughts. Every one can realize this from his own experience. This is because so-called abstract reason is perceptive thought and can take place only by means of perceptions. Perceptions we can designate and hold only by means of names. Every attempt to broaden our minds, every attempt to advance our knowledge must begin by distinguishing and classifying by means of names or by giving to the old ones a more precise meaning. Language is the body of the mind, the material by which all human science can be built up. The difference between the human mind and the animal mind was very aptly shown by Schopenhauer. This citation is quoted by Kautsky in his “Ethics and the Materialist Conception of History” (pages 139–40 English Translation). The animal’s actions are dependent upon visual motives, it is only by these that it sees, hears or observes in any other way. We can always tell what induced the animal to do this or the other act, for we, too, can see it if we look. With man, however, it is entirely different. We can not foretell what he will do, for we do not know the motives that induce him to act; they are thoughts in his head. Man considers, and in so doing, all his knowledge, the result of former experience, comes into play, and it is then that he decides how to act. The acts of an animal depend upon immediate impression, while those of man depend upon abstract conceptions, upon his thinking and perceiving. Man is at the same time influenced by finer invisible motives. Thus all his movements bear the impress of being guided by principles and intentions which give them the appearance of independence and obviously distinguishes them from those of animals.