60 HUME I 



cursory attention to the ways and works of the 

 lower animals suggests a comparative anatomy 

 and physiology of the mind ; and the doctrine of 

 evolution presses for application as much in the 

 one field as in the other. 



But there is more than a parallel, there is a 

 close and intimate connection between psychology 

 and physiology. No one doubts that, at any rate 

 some mental states are dependent for their exist- 

 ence on the performance of the functions of 

 particular bodily organs. There is no seeing 

 without eyes, and no hearing without ears. If 

 the origin of the contents of the mind is truly a 

 philosophical problem, then the philosopher who 

 attempts to deal with that problem, without 

 acquainting himself with the physiology of sensa- 

 tion, has no more intelligent conception of his 

 business than the physiologist, who thinks he can 

 discuss locomotion, without an acquaintance with 

 the principles of mechanics ; or respiration, with- 

 out some tincture of chemistry. 



On whatever ground we term physiology, science, 

 psychology is entitled to the same appellation ; 

 and the method of investigation which elucidates 

 the true relations of the one set of phenomena will 

 discover those of the other. Hence, as philosophy 

 is, in great measure, the exponent of the logical 

 consequences of certain data established by 

 psychology ; and as psychology itself differs from 

 physical science only in the nature of its subject- 



