It thus appears, that the names generally of what are called the objects of sense are equivocal; and whereas it would have been a security against confusion to have been provided with appropriate names, one, in each instance, for the Sensation, and one for the Idea, the same name has been made to serve as the mark for both. The term horse is not only made to stand for the sensations of sight, of hearing, of touch, and even of smell, which give me occasion for the use of the term horse; but it stands also for the ideas of those sensations, as often as I have occasion to speak of that cluster of ideas which compose my notion of a horse. The term tree denotes undoubtedly the Idea in my mind, when I mean to convey the idea tree into the mind of another man; but it also stands for the sensations whence I have derived my idea of a tree. Thus, too, if I mean to name my simple ideas; those, for example, of sight; I have no other names than red, blue, violet, &c.; but all these are names of the sensations. When forced to distinguish them, I must use the awkward expressions, my sensation of red, my idea of red. Again; sound of a trumpet, is the name, as well of the sensation, as the idea; flight of a bird, the name, as well of the sensation, as the idea; light the name as well of the sensation as the idea; pain {140} the name as well of the sensation as the idea; heat the name as well of the sensation as the idea.[43] [Editor's footnote 43: In strict propriety of language all these are names only of sensations, or clusters of sensations; not of ideas. A person studious of precision would not, I think, say heat, meaning the idea of heat, or a tree, when he meant the idea of a tree. He would use heat as the name only of the sensation of heat, and tree as the name of the outward object, or cluster of sensations; and if he had occasion to speak of the idea, he would say, my idea (or the idea) of heat; my idea (or the idea) of a tree.--_Ed._] As we have remarked, in regard to SENSATIONS, singly, or in clusters, that they are too numerous to receive names but in classes, that is names common to every individual of a class, the same is obviously true of the IDEAS. The greater number of names of Sensible Ideas are names of classes: man is the name of a class; lion, horse, eagle, serpent, and so on, are names of classes. Ideas, of the third class, those which the mind forms arbitrarily, are innumerable; because the combinations capable of being formed of the numerous elements which compose them, exceed computation. All these combinations cannot receive names. The memory can manage but a moderate number. Of possible combinations, therefore, a small proportion must be selected for naming. These, of course, are the combinations which are suggested by the occasions of life, and conduce to the ends which we pursue.