68 BIOLOGICAL ASPECTS OF HUMAN PROBLEMS 



accept the latter view. If, however, we take the 

 position that there are not, in fact, two entirely inde- 

 pendent states of reality, we are at once confronted 

 with the necessity of deciding that the basis of mind 

 is either wholly material or wholly spiritual. But 

 there are obvious difficulties connected with either 

 of these assumptions. These difficulties have led 

 to the promulgation of a doctrine which is known as 

 psychophysical parallelism, which has its roots in 

 the dualism of Descartes, Spinoza, and Leibnitz. 

 According to this doctrine, each physical change in 

 the nervous system is accompanied on the mental 

 side by a concomitant change in the psychical system, 

 to which we give the name consciousness. The 

 converse is also true; that is, every mental change 

 is accompanied by alterations in the physical state. 

 The relation between the mental state and the bodily 

 state is thus conceived as one of parallelism, coin- 

 cidence, correspondence, or concomitance. The at- 

 tractiveness of this theory lies in the fact that it 

 does not force us to assume the existence of any 

 causal interaction at all between mind and body. 

 The facts of consciousness are accounted for equally 

 well by maintaining that such causal relations as 

 exist lie within the physical series of events or within 

 the psychical series. W. K. Clifford stated this 

 view with the help of the following well-known 

 illustration: when we say "a feeling of chill made 

 a man run," what we mean is "the nervous 

 disturbance which coexisted with that feeling of chill 



