Nature of Evolutionary Progress 43 



opinion. The preceding conditions include a certain 

 mental state and a certain physical condition; that 

 is, a condition perceived by the "inner" view, and one 

 perceived by the "outer" view. We wish to determine 

 to which of these conditions the action is due. We 

 wish to know whether withdrawing the hand from the 

 flame is due to the high temperature and accompany- 

 ing physical changes in the hand or to the pain that 

 occurs. 



To answer this question, we must separate the two 

 things. We must separate the physical condition from 

 the sensation that occurs with it, and so find out 

 whether it is really true, as the mechanist holds, that 

 the same physical condition without the sensation 

 would produce the same result, would, in this case, 

 produce the withdrawal of the hand. And to discover, 

 on the other side, whether the sensation is the exclu- 

 sive agent, one must isolate it from its physical ac- 

 companiment and try it alone. 



But these experiments have but to be proposed in 

 order to reveal that they are impossibilities. When a 

 certain sensation, emotion, or other mental state oc- 

 curs, there is also a certain characteristic physical 

 condition of the organism which is different from the 

 physical condition existing when this sensation or 

 emotion does not occur. To every difference in mental 

 state corresponds a difference in physical state. One 

 cannot remove the sensation or emotion and leave the 

 physical condition as it was. And one cannot change 

 the characteristic physical situation without altering 

 the sensation or emotion. The particular sensation or 



