240 THE PROBLEM OF BODY AND MIND 



This amounts to a denial of the existence of the physical 

 world and of the possibility of science; it is the non-pos- 

 sumus of solipsism. 



(IV) A fourth view common as a working-hypothesis 

 at least goes by the name of psycho-physical parallelism. 

 It admits the reality of both mental and cerebral processes, 

 but regards them as concomitants merely, without inter- 

 action, two parallel causal chains, each complete in itself. 

 We may think of two watches tied together, keeping perfect 

 time, but constructed on different principles and using dif- 

 ferent notations. This view was subjected to what seems 

 to us destructive criticism in Professor Ward's first course of 

 Gifford Lectures on " Naturalism and Agnosticism " ; but 

 it is still held by some psychologists of distinction, either 

 simply as a convenient way of formulating the facts, or 

 with a metaphysical theory behind it namely, an idealistic 

 view of material phenomena. 



Besides psycho-physical parallelism there are in the field 

 three possible theories. One is much favoured by philoso- 

 phers (V) the theory of psychical monism. Another view, 

 (VI) the soul-theory or animism, does not seem to be fa- 

 voured by many philosophers or by many scientific investiga- 

 tors, but may be true for all that. The remaining theory, 

 much favoured by biologists, is (VII) the two-aspect or iden- 

 tity hypothesis. It seems to us that each of these theories has 

 its particular advantages and its particular difficulties, and 

 that a decision must at present be left with the individual 

 according to his personal experience. In our judgment the 

 biological facts mostly favour the two-aspect theory, but we 

 have no assurance that it is the most valid. 



(V) Psychical Monism. According to the doctrine of 

 psychical monism, conscious process is the only reality, and 



