Let us now, proceeding to the simplest cases first, and by them expounding such as are more complicated, suppose that our name of one individual is applied to another individual. Let us suppose that the word, foot, has been first associated in the mind of the child with one foot only; it will in that case call up the idea of that one, and not of the other. Here is one name, and one thing named. Suppose next, that the same name, foot, begins to be applied to the child's other foot. The sound is now associated not constantly with one thing, but sometimes with one thing, and sometimes with another. The consequence is, that it calls up sometimes the one, and sometimes the other. Here two things, the two feet, are both of them associated with one thing, the name. The one thing, the name, has the power of calling up both, and in rapid succession. The word foot suggests the idea of one of the feet; this foot with its name, is a complex idea; and this complex idea suggests its like, the other foot with its name. This is a peculiar and a highly important case of association; but not the less simple and indisputable. We have already sufficiently exemplified the two grand cases of the formation of complex ideas by association;--that in which the ideas of synchronous sensations are so concreted by constant conjunction as to appear, though numerous, only one; of which the ideas of sensible objects, a rose, a plough, a house, a ship, are examples;--and that in which the ideas of successive sensations are so concreted; of which, the idea of a {264} tune in music, the idea of the revolution of a wheel, of a walk, a hunt, a horse-race, are instances. It is easy to see wherein the present case agrees with, and wherein it differs from, those familiar cases. The word, man, we shall say, is first applied to an individual; it is first associated with the idea of that individual, and acquires the power of calling up the idea of him; it is next applied to another individual, and acquires the power of calling up the idea of him; so of another, and another, till it has become associated with an indefinite number, and has acquired the power of calling up an indefinite number of those ideas indifferently. What happens? It does call up an indefinite number of the ideas of individuals, as often as it occurs; and calling them up in close connexion, it forms them into a species of complex idea.