I 



LIFE AND MIND 



between the external phenomena ; but it is 

 the connection between these two connections, A 

 psychological proposition is necessarily com- 

 pounded of two propositions, of which one con- 

 cerns the subject and the other concerns the 

 object ; and cannot be expressed without the 

 four terms which these two propositions imply. 

 The distinction may be best explained by sym- 

 bols. Suppose that a and b are two related 

 manifestations in the environment — say, the 

 colour and taste of a fruit ; then, so long as 

 we contemplate their relation by itself, or as 

 associated with other external phenomena, we 

 are occupied with a portion of physical science. 

 Now suppose that x and y are the sensations 

 produced in the organism by this peculiar light 

 which the fruit reflects, and by the chemical 

 action of its juice on the palate ; then, so long 

 as we study the action of the light on the retina 

 and optic centres, and consider how the juice 

 sets up in other centres a nervous change known 

 as sweetness, we are occupied with facts belong- 

 ing to the science of physiology. But we pass 

 into the domain of psychology the moment we 

 inquire how there comes to exist within the or- 

 ganism a relation between x and y that in some 

 way or other corresponds to the relation be- 

 tween A and B. Psychology is exclusively con- 

 cerned with this connection between a b and 



113 



