BEGINNINGS OF INTELLIGENCE 171 



movements. The latter problem is one whose solution 

 appears hopeless. If we accept the doctrine of psycho- 

 physical parallelism in any of its forms, we must deny that 

 psychic states are, strictly speaking, the causes of physical 

 changes. Why then should pleasure be connected with one 

 kind of activity and pain with another? Why 'not just the 

 reverse? This problem is, I believe, insoluble, because it is 

 a question of the relation of the physical and the psychical; 

 it is of essentially the same nature as the question why one 

 kind of retinal stimulation produces a sensation of red and 

 another a sensation of green. Physical and psychical states 

 are correlated in particular ways; this we accept as a matter 

 of observed connection. But why a certain kind of brain 

 vibration is associated with a state of consciousness we call 

 a sensation of red instead of some other state is a question 

 upon which we may intend our minds indefinitely without 

 the least profit. If we adopt any other theory of the relation 

 of mind and body we are in no way better off. If we have 

 to do with a preordained connection of pleasure with certain 

 physiological activities and pain with certain others, this 

 connection is no more intelligible if we admit the interaction 

 of psychical and physical states than it is under the theory 

 of parallelism. We can only say that such is the observed 

 relation of the phenomena. 



What is feasible to attempt to solve is the problem of the 

 adaptive modification of behavior which we may say is the 

 objective side of the pleasure- pain process. We are dealing 

 with a series of physiological reactions and how they come 

 to be modified. We may assume that psychical states enter 

 into the chain of causes and effects that make up an animal's 

 behavior, but it is not clear that such an assumption throws 

 the least light upon our problem, and it is open to serious 

 objections on both scientific and metaphysical grounds. We 



