50 HABIT AND INTELLIGENCE. [cHAP. 



. the two may acquire a habit of always accompanying each 

 other, so that the sight of the face will recall the voice into 

 conscious memory, and the sound of the voice will simi- 

 larly recall the sight of the face. I have spoken ahove of 

 Groups of u sensations, or groups of sensations." The sound of a voice 

 is a single sensation ; the impression of a man's face on the 

 sense of sight is a group of sensations ; but once a group 

 of sensations has become familiar, it is capable of becoming 

 the subject of associations, just like a simple sensation. 



In the case of association just mentioned, the ideas of 

 two things become associated in our consciousness, because 

 the things themselves have been associated in our expe- 

 rience by contiguity to each other, either in space or in 

 Assoeia- time ; and association produced in this way is called asso- 

 ti"'^.^y. ciation by contiguity. Association is produced in another 

 con i„ui y, ^^^^ ^yiiici^^ though quite as familiar, is not quite so easy 

 to analyse into its elements, so as to prove it to be a case 

 and by re- f ^^^ jg^^ ^f habit. I mean association by resemblance ; 



cp Tin il I fl Tl f P 



' as, for instance, when the sight of a good portrait recalls to 



mind the face it resembles. Association by resemblance 



and association by contiguity are sometimes spoken of as 



if they were both ultimate facts of the mental nature ; but 



both cases I think it can be shown that they are both to be referred 



of ^^^^ . to the same principle of association, though under different 



same prm ^-^^^^g^^j^^^gg^ ^^(j ^j^at they are both alike cases of the 



law of habit. In order to explain the fact of association by 



resemblance as a case of mental habit, it is better to speak, 



not of objects having the kind of likeness that a face and 



its portrait have to each other, but of objects so nearly 



alike as to be indistinguishable ; as, for instance, two 



uncut copies of the same book. If I see a book at a 



friend's house, and this recalls to my memory that I have 



seen the same book — that is to say, a precisely similar 



]30ok— in a bookseller's shop, by what mechanism of asso- 



Explana- ciation is the recollection effected? It is to be thus 



tion of as- explained : mv first view and my second view of the book 



by resem- are two distinct incidents, partly alike and partly unlike^ 



blance: ^-^.^^ -^ ^^^^^ y^^ ^^^ copies of the book were exactly 



similar, unlike in that the places and other circumstances 



