2 s2 POPULAR SCIENCE MONTHLY. 



HUMAN AND OTHER FORMS OF CONSCIOUSNESS. 



BY Dr. HENRY RUTGERS MARSHALL, 



NEW YORK. 



WHEN we are trying to think clearly we are wont to be disturbed 

 if our friends accuse us of wandering from the sure grounds 

 of science and entering the jungle of metaphysics. 



Nevertheless, it must be acknowledged that, without realizing it, all 

 men do really devote a fair proportion of their thought to problems 

 which, strictly speaking, are of a metaphysical nature : and the question 

 as to the relation of ' mind to body/ which has an entrancing interest 

 for so large a body of thoughtful people, is clearly one in reference to 

 which no one can take a definite position without at the same time 

 assuming an attitude in relation to fundamental metaphysical prin- 

 ciples. 



We turn to the skilled biologist in these days for expert opinion 

 in this matter, only to find him tarred with the same brush; for as a 

 biologist the problem before him has properly no significance. As a 

 biologist he is concerned with forms of ' animal behavior,' to use Lloyd 

 Morgan's happy phrase. If he takes into consideration in any way the 

 consciousness of animals, in that fact he assumes the attitude of the 

 metaphysician. It is clearly because he takes this step into the meta- 

 physical domain, without realizing it, that we find among those 

 psychological biologists who consider the consciousness of animals so 

 wide a divergence of opinion as to the conditions under which such 

 consciousness exists. 



But, as I have said, this matter is of great interest to all of us, and 

 is looked upon as deserving our serious consideration. It is quite 

 worth our while then to acknowledge frankly that we are dealing with 

 a metaphysical problem, and at the start to make a rather deep plunge, 

 laying aside for the moment all thought of the consciousness of animals, 

 and asking ourselves what ground we have for our every-day assump- 

 tion that other men are conscious as we ourselves are. 



The ready answer seems to be that they tell us of their conscious 

 states. But evidently this reply does not suffice us, for it becomes 

 very clear upon consideration that no amount of hearsay evidence 

 would serve to convince us of the fact that these other men are con- 

 scious did we not note that our activities, which are very like their 

 activities, are accompanied in our experience by modifications in our 



