Nature of Evolutionary Progress 45 



that the same physical condition without the sensa- 

 tion or opinion or other mental state would produce 

 the same result, for the same physical condition never 

 occurs without the mental state. And it cannot be as- 

 serted that the mental state alone is the cause of the 

 action, for the mental state does not occur alone. The 

 two stand on exactly the same footing experimentally 

 and in science; if one is a cause of action, so is the 

 other. The mental state and its characteristic physi- 

 cal condition are inseparable; experimentally and 

 practically they are identified. We may, without prac- 

 tical or experimental error follow the example of those 

 that call them two aspects of the same situation,^ the 

 same situation viewed in two different ways. It is this 

 situation that is the cause of the action. In speaking 

 of this cause, we may call it by either of its two as- 

 pects, and one is as correct as the other. For experi- 

 mental science, the mental state is the cause of action 

 on the same basis as is the correlative physical con- 

 dition, for the two are one. My opinion is the cause 



this it is sometimes ar^ed that the purpose when it did occur 

 played no role. But this conclusion is experimentally fallacious as 

 was the one before mentioned. For in all such comparisons, as in all 

 cases where the same final result is produced in different ways, we 

 have the following conditions : 



(1) The antecedent physical condition differs in the two cases, 

 that is, when a purpose is present and when it is not. 



(2) The action itself differs in details in the two cases. There- 

 fore this gives no evidence that the same physical state that was 

 in the first instance accompanied by a purpose would produce 

 the same result when not accompanied by a purpose, for that same 

 physical state does not occur without the purpose. These con- 

 siderations apply to all arguments of this nature. 



1 See, for example, H. C. Warren, "The Mental and the Physi- 

 cal," The Psychological Review, XXI (1914). 



