So much, then, for ideas as particular and general. Next, the term abstract has been used by different psychologists in different senses. For my own part, I will adhere to the usage of Locke in the passage above quoted, which is the usage adopted by the majority of modern writers upon these subjects. According to this usage, the term “abstract 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 does 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.[16]