290 POPULAR SCIENCE MONTHLY. 



experiment which we venture upon with the greater confidence, because 

 of the success of our present meeting in Pittsburgh. 



For my address this evening I have chosen the theme: 'The Prob- 

 lem of Consciousness in its Biological Aspects.' I hope both to con- 

 vince you that the time has come to take up consciousness as a strictly 

 biological problem, and also to indicate the nature of that problem, 

 and some of the actual opportunities for investigating it. It is neces- 

 sary to begin with a few words on the philosophical interpretation. We 

 shall then describe the function of consciousness in animal life, and 

 consider its part in the evolution of animals and of man. The views 

 to be stated suggest certain practical recommendations, after presenting 

 which I shall conclude by offering an hypothesis of the relation of con- 

 sciousness to matter and force. 



Consciousness is at once the oldest problem of philosophy and one 

 of the youngest problems of science. The time is not yet for giving a 

 satisfactory definition of consciousness, and we must fain content our- 

 selves with the decision of the metaphysician, who postulates conscious- 

 ness as an ultimate datum or concept of thought, making the brief 

 dictum cogitOj ergo sum the pivot about which his system revolves. I 

 have endeavored vainly to discover by reading and by questioning those 

 philosophers and psychologists whom I know, some deeper analysis of 

 consciousness, if possible, resolving it into something more ultimate. 



Opinions concerning consciousness are many and often so diverse 

 as to be mutually exclusive, but they may be divided into two principal 

 classes. The first class includes all those views which make of con- 

 sciousness a real phenomenon; the second, those views which interpret 

 it as an epiphenomenon. We are, I think practically all, agreed that 

 the fundamental question is : Does or does not consciousness affect 

 directly the course of events? — or, stated in other words, is conscious- 

 ness a true cause ? In short, we encounter at the outset the problem of 

 free-will; of which more later. 



The opinion that consciousness is an epiphenomenon has gained 

 renewed prominence in recent times, for it is, so to speak, a collateral 

 result of that great movement of European thought which has culmi- 

 nated in the development of the doctrine of monism. Monism itself 

 is postulated chiefly upon the two greatest discoveries of the nineteenth 

 century — the law of the conservation of energy, and the law of the 

 evolution of species. Both laws establish a greater unity in the phe- 

 nomena of the universe than mankind had previously been able to 

 accept. In the physical world, instead of many forces, we now recog- 

 nize only one force, which assumes various forms of energy; and in the 

 living world we recognize one life, which manifests itself in many 

 types of form. With these two unities in mind, what could be nearer 

 than the thought that the unity goes still deeper, and that the phe- 



