THE EVOLUTION OF MIND 



degrees of permeability. Those which have 

 been oftenest traversed will be the most perme- 

 able, and those which are traversed only at rare 

 intervals will be but slightly permeable ; while 

 the passage of a nervous discharge in a new di- 

 rection will involve the differentiation of a new 

 line of transit. 



Now subjective psychology furnishes us with 

 an exact parallel to this state of things. The 

 profound analysis of conscious changes carried 

 on by the English school of psychology since 

 the time of Hobbes, and accepted by the Kan- 

 tian school in all save a few very important 

 instances — which we shall presently see to be 

 similarly explicable — has ended in the conclu- 

 sion that states of consciousness cohere with a 

 strength dependent upon the frequency with 

 which they have been repeated in experience. 

 In other words, "the persistence of the connec- 

 tion between states of consciousness is propor- 

 tionate to the persistence of the connection be- 

 tween the agencies to which they answer." This 

 fundamental law of association is illustrated by 

 such familiar truths as the following : " that 

 phenomena wholly unrelated in our experience, 

 we have no tendency to think of together ; that 

 where a certain phenomenon has occurred in 

 many relations, we usually imagine it as recur- 

 ring in the relation in which it has most fre- 

 quently occurred ; that when we have witnessed 



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