24 MENTAL EVOLUTION IN MAN. 



idea " is practically synonymous with the term " general 

 idea." For the process of abstraction consists in mentally 

 analysing the complex which is presented by any given 

 object of perception, and ideally extracting those features or 

 qualities upon which the attention is for the time being 

 directed. Even the most individual of objects cannot fail to 

 present an assemblage of qualities, and although it is true 

 that such an object could not be divided into all its 

 constituent qualities actually, it docs admit of being so 

 divided ideally. The individual man whom I know as John 

 Smith could not be disintegrated into so much heat, flesh, 

 bone, blood, colour, &c., without ceasing to be a man at all ; 

 but this does not hinder that I may ideally abstract his heat 

 (by thinking of him as a corpse), his flesh, bones, and 

 blood (by thinking of him as a dissected "subject"), his white 

 colour of skin, his black colour of hair, and so forth. Now, 

 it is evident that in the last resort our power of forming 

 general ideas, or concepts, is dependent on this power of 

 abstraction, or the power of ideally separating one or more 

 of the qualities presented by percepts, i.e. by objects of 

 particular ideas. My general idea of heat has only been 

 rendered possible on account of my having ideally abstracted 

 the quality of heat from sundry heated bodies, in most of 

 which it has co-existed with numberless different associations 

 of other qualities. But this does not hinder that, wherever 

 I meet with that one quality, I recognize it as the same ; and 

 hence I arrive at a general or abstract idea of heat, apart 

 from any other quality with which in particular cases it may 

 happen to be associated.* 



This faculty of ideal abstraction furnishes the conditio sine 



* Hence, the only valid distinction that can be drawn between abstraction and 

 generalization is that which has been drawn by Hamilton, as follows : " Abstrac- 

 tion consists in concentration of attention upon a particular object, or particular 

 quality of an object, and diversion of it from everything else. The notion of the 

 figure of the desk before me is an abstract idea — an idea that makes part of the 

 total notion of that body, and on which I have concentrated my attention, in order 

 to consider it exclusively. This idea is abstract, but it is at the same time 

 individual : it represents the figure of this particular desk, and not the figure of 

 any other body." Generalization, on the other hand, consists in an ideal 



