46 The Universe and Life 



of my voting in a certain way; and so is also the 

 physical condition that goes with that opinion, for 

 the two are experimentally the same thing. 



Thus in describing the causes of the actions of men 

 or other organisms, we may use either the mental 

 state or the physical condition, as is most convenient. 

 In dealing with lower organisms or with simple re- 

 actions, it will be most convenient and most helpful to 

 employ the physical condition. The student of physi- 

 ology may properly attribute the withdrawal of the 

 finger from the flame to the rise in temperature of 

 the nerve endings in the skin, although he cannot 

 properly deny that the accompanying pain has a role 

 in the matter. For explanation of the behavior of 

 man, particularly of his more complex actions, it will 

 commonly carry more insight if one refers to the 

 mental states. For explanation of why I voted for 

 Hoover in place of Roosevelt or vice versa, or for ex- 

 plaining why I say what I do in these lectures, the 

 statement in terms of physical conditions is extremely 

 involved, uncertain, and unintelligible. So it is better 

 in such cases to refer to thoughts and opinions and 

 purposes as accounting for the actions. Both have the 

 same degree of scientific justification, both are fully 

 justified. 



We conclude then that, for experimentation and 

 therefore for science, mental states have effect on ac- 

 tion. The ground for this assertion is of the same 

 character as for the assertion that any other agency 

 has effect on action. Sensations, emotions, ideas, pur- 



