February 21, 1913] 



SCIENCE 



277 



nature, and natural history of the self. 

 "Know thyself" means know thyself as 

 a man, a member of the human race. And 

 the natural history of the individual mind 

 or soul, can not be described, much less 

 explained, without interpreting it all in 

 the light of what we have learned of the 

 natural history of the race. 



These remarks may suffice as introduc- 

 tory to an answer — confessedly fragmen- 

 tary and full of assumptions which need 

 proofs from sources lying outside our 

 theme — to the two questions raised above. 

 The first of these, you will remember, was 

 this: What have modern psychology and 

 anthropology to say about the view which 

 identifies knowledge with sense-perception, 

 and about its allied theory of knowledge? 



If by perception by the senses we under- 

 stand the mere fact that certain sensations 

 form groups and sequences in conscious- 

 ness, which have more or less of persistence 

 and regularity, the banter of the wise 

 Socrates as addressed to the youthful The- 

 ffitetus is not inappropriate in our own day : 



I say nothing against his doctrine, that what 

 appears to each one to be, really is to each one, 

 but I wonder that he did not begin his great work 

 on Truth with a declaration that a pig or a dog- 

 faced baboon or some other strange monster which 

 has sensation, is the measure of all things; then, 

 when we were reverencing him as a god, he might 

 have condescended to inform us that he was no 

 wiser than a tadpole and did not even aspire to be 

 a man — would not this have produced an over- 

 powering effect? For if truth is only sensation, 

 and one man's discernment is as good as an- 

 other's, and no man has any superior right to 

 determine whether the opinion of any other is true 

 or false, but each man, as we have several times 

 repeated, is to himself the sole judge, and every- 

 thing that he judges is true and right, why should 

 Protagoras himself be preferred to the place of 

 instruction, and deserve to be well paid, and we 

 poor ignoramuses have to go to him, if each one 

 is the measure of his own wisdom? 



Even if we say, I do not mean the sensa- 

 tions of a tadpole, or even of a dog-faced 



baboon, but the sensations of a man, we do 

 not establish in perception by the senses 

 alone a ground for science. The only way 

 we can know what the baboon actually sees, 

 or otherwise perceives through Jiis senses, 

 is by the use of our powers of perception 

 as applied to the behavior of the baboon. 

 Our claim to superiority over the baboon, 

 even if we are descended from him in more 

 or less direct line, is based upon the con- 

 fidence that our perceptions, as forming a 

 ground for a scientific knowledge of things, 

 and perhaps for a theory of the universe, 

 are more trustworthy and comprehensive 

 than are his. The old-fashioned way of 

 putting this truth was not so bad after all : 

 Man may be an animal; indeed, he un- 

 doubtedly is an animal; but man is a 

 rational animal. 



Psychology, with its recent more subtle 

 analyses, as made possible by the experi- 

 mental method, has made it perfectly clear 

 that sense-perception in the case of the 

 human individual is an exceedingly com- 

 plex development, involving all man's nat- 

 ural and acquired capacities and forms of 

 functioning. Into every act of the senses 

 which gives us intimations, or assured 

 knowledge, of real existences and actual 

 happenings, there enter many instinctive 

 or acquired faiths, leaps to judgment or 

 more slowly formed inferences, emotional 

 factors expressive of doubt, or certainty, or 

 negation, habits favoring or prejudiced 

 against this or that conclusion, fleeting or 

 more fixed associated images of memory or 

 of fancy, and formal or regulating prin- 

 ciples, the so-called categories or "innate 

 ideas" of the earlier philosophy. But 

 above all, if the process of sense-perception 

 terminates in conviction of the reality of 

 the object perceived, or the actuality of the 

 event observed, then this object, or those 

 things concerned in the event, are made 

 the centers of forces that justify us in 



