PSYCHOLOGICAL SCIENCE 83 



pany them. Such inquiries are of fundamental 

 importance to mankind, but they are problems of 

 that branch of philosophy known as metaphysics, 

 and are not problems which psychology or any 

 other science can answer or need ask. Just as 

 the function of physical science is to construct a 

 mental model of nature seen in a physical light, and 

 the function of biology is to represent it in a bio- 

 logical light, so psychology constructs a mental model 

 of that part of nature which involves mind from its 

 own special point of view. Its function is to con- 

 struct a consistent model, not to seek the answer to 

 the more fundamental question whether that model 

 corresponds completely with reality. That inquiry 

 is reserved for metaphysics. Moreover, psychology 

 cannot even rightly investigate the connection be- 

 tween its own model and that of physics or biology. 

 They are, so to speak, on different planes, and cannot 

 of themselves get into contact. The true connection, 

 or want of connection, between them is a part of the 

 study of reality that is a problem of metaphysics. 



Metaphysicians have formed four hypotheses on 

 this particular point. There is the metaphysical 

 theory of psycho-physical parallelism, which exalts 

 to the state of an ultimate truth that parallelism 

 of two independent series which psychologists take 

 merely as a convenient scientific working hypothesis. 

 According to this dualistic theory, our conscious 

 thoughts and our neural changes are for ever keeping 



