THE ANIMAL MIND 



CHAPTER I 



THE DIFFICULTIES AND METHODS OF COMPARATIVE 

 PSYCHOLOGY 



i. Difficulties 



[THAT the mind of each human being forms a region inac- 

 cessible to all save its possessor, is one of the commonplaces 

 of reflection. His neighbor's knowledge of each person's 

 mind must always be indirect, a matter of inference. \ How 

 wide of the truth this inference may be, even under the most 

 favorable circumstances, is also an affair of everyday ex- 

 perience: each of us can judge his fellow-men only on the 

 basis of his own thoughts and feelings in similar circum- 

 stances, and the individual peculiarities of different members 

 of the human species are of necessity very imperfectly com- 

 prehended by others. The science of human psychology 

 has to reckon with this unbridgable gap between minds as 

 its chief difficulty. The psychologist may look into his own 

 mind and study its workings with impartial insight, yet he 

 can never be sure that the laws which he derives from such 

 a study are not distorted by some personal twist or bias. For 

 example, it has been suggested that the philosopher Hume 

 was influenced by his tendency toward a visual type of 

 imagination in his discussion of the nature of ideas, which 

 to him were evidently visual images. As is well known, the 

 experimental method in psychology has aimed to minimize 



