When a person who is conscious of an idea is striving to revive a related idea which he has forgotten, he presents an example of memory in the making; for he is striving to revive the yet incomplete organic union between them, which was the result of the original apprehension of their relations, and which, when complete, will cause the one idea to recall the other instantly and without the least effort, just as a single sensation of an object at once revives the cluster of sensations which are combined in the perception of it. The process of intellectual development consists in the mental organization of related ideas, as internal representatives of external relations in nature, and in making this organization so complete that a number of associated ideas shall act like a single idea, being combined into a complex product and recalled instantly and without conscious effort, just as a complex movement is. Then the memory is so complete that we must cease to call it memory, because it is unconscious. In fact, spontaneous recollection is at an end when involuntary memory begins, and involuntary memory merges gradually into a reproduction of former mental experiences which is as completely automatic as the habitual movements of our daily life. And well it may be; for the same organic property of nerve element--indeed, I might say, the same fundamental property of organization--is at the bottom of both. Thus much concerning the nature and function of memory. Upon its basis rests the possibility of mental development, in which there are, as we have already seen, the organic registration of the _simple_ ideas of the senses; the assimilation of the like in ideas which takes place in the production or evolution of _general_ ideas; the assimilation, of the properties common to two or more general ideas into an _abstract_ idea; the special organization or differentiation, or discrimination, of unlike ideas; the organic combination of the ideas derived from the different senses into one _complex_ idea, with the further manifold combinations of complex ideas into what Hartley called _duplex_ ideas. In fact, no limit is assignable to the complexity of combinations which may go to the formation of a compound idea. Take, for example, the idea of the universe. But how comes it to pass that a new imaginative creation of the mind, to which nothing in nature answers, is effected? By the same process fundamentally as that by which our general and abstract ideas are formed. For when we consider the matter, it appears that there are no actual outside existences answering to our most abstract ideas, which are, therefore, so far new creations of the mind; in their formation there is a blending or coalescence of the like relations in two concrete ideas--the development of a _concept_, there is, as it were, an extraction of the essential out of the particular, a sublimation of the concrete; and, by the creation of a new world in