EH. xvi.] THE EVOLUTION OF MIND. 147 



like the human biain, we may expect to find a countless 

 number of transit-lines, of all degrees of permeability. 

 Those which have been oftenest traversed will be the most 

 permeable, and those which are traversed only at rare 

 intervals will be but slightly permeable ; while the passage 

 of a nervous discharge in a new direction will involve the 

 differentiation of a new line 01 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 psy 

 chology since the time of Hobbes, and accepted by the 

 Kantian school in all save a few very important instances 

 which we shall presently see to be similarly explicable 

 has ended in the conclusion that states of consciousness 

 cohere with a strength dependent upon the frequency with 

 which they have been repeated in experience. In other 

 words, &quot; the persistence of the connection between states of 

 consciousness is proportionate to the persistence of the con 

 nection between the agencies to which they answer. This 

 fundamental law of association is illustrated by such familiar 

 truths as the following : &quot; that phenomena wholly unrelated 

 in our experience, we have no tendency to think of together; 

 that where a certain phenomenon has occurred in many rela 

 tions, we usually imagine it as recurring in the relation in 

 which it has most frequently occurred ; that when we have 

 witnessed many recurrences of a certain relation we come to 

 have a strong belief in that relation ; that if a relation has 

 been daily experienced throughout life with scarcely an 

 exception, it becomes difficult for us to conceive it as other 

 wise to break the connection between the states of con- 

 sciousnes/i representing it; and that where a relation has 

 been perpetually repeated in our experience with absolute 

 uniformity, we are entirely disabled from conceiving the 

 negation of it.&quot; l 



1 Spencer, Principles of Fsyclioloj ?/, voL i. p. 421 



L 2 



