When we consider our problem from a purely psychological point of view, we have to follow out the same lines of thought which we pursued in our discussion of the anatomical problem. We must try to enumerate clearly the typical differences between the human mind and the animal mind, which must serve as the background of our discussions. In the treatment of the psychic differences between civilized man and primitive man, we must distinguish the two problems of differences in cultural state of members of the same race, and differences in characteristics of different races; in other words, the problems of environmental influences and of influences of heredity. For the purposes of our investigation, we do not need to enter deeply into a discussion of the first-named problem, the differences between the minds of the animal and of man. The differences are so striking that little or no diversity of opinion exists. The two outer traits in which the distinction between the minds of animal and of man finds expression are the existence of organized articulate language in man, and the use of utensils of varied application. Both of these are common to the whole of mankind. No tribe has ever been found that does not possess a well-organized language; no community that does not know the use of instruments for breaking, cutting, or drilling, the use of fire and of weapons with which to defend themselves and to obtain the means of living. Although means of communication by sound exist in animals, and although even lower animals seem to have means of bringing about co-operation between different individuals, we do not know of any case of true articulate language from which the student can extract abstract principles of classification of ideas. It may also be that higher apes employ now and then limbs of trees or stones for defence, but the use of complex utensils is not found in any representative of the animal series. Only in the case of habitations do we find an approach to more complex activities, which, however, remain absolutely stable in each species,—as we say, instinctive,—and bear no evidence of any individual freedom of use, which constitutes the primary character of human inventions. The origin of the instinctive activities of animals which lead to the construction of complex mechanical devices is still a hidden secret; but the relation of the individual of the species to these activities differs from that of man to his inventions in the complete lack of freedom of control.