Appendix (c) It may not be unimportant, for many reasons, to ascertain precisely the meaning of the terms, unity and identity. Our notion, then, of unity is derived not from the real and actual unity of a thing, for it is an idea not immediately derived from the senses; but flows first from the unity of the mind itself, and secondly from one of its complex operations. Nothing can be one to the eye, since all objects of vision are contiguous to each other, and it depends on the arbitrary action of the mind, to cut up that extended plain,which is pictured on our retina, into different portions, by checking its continuous perceptions, with the assistance of those lines of light and shade with which nature has pencilled it out. But a sound, or sensation, or taste, or smell, or colour distinct from figure, is to us one idea; that is, it separately and distinctly occupies the mind, it is perfectly indivisible into successive sensations; and is, in fact, the mind itself in one state. And that groupe of qualities or attributes, is also one, which the mind in perceiving, runs over one after another, anticipating the second before the first is over, till it has passed through them all, and possessing no other from association or perception, to add to the list, it comes, as it were, to a full stop, and shuts up all these ideas into one case. And it is from this power which the mind has of stopping where it likes in running over ideas, of cutting off the connexion between them, and considering each separately, that we derive, as was before observed, ourinfinite number of abstract substantives. The terminations of these abstract words serving as so many hints to us to break off the ideas contained in them, from the other ideas which we had usually added on to them. And though from the natural tendency of the mind to pass on as usual to these consecutive states, there is a great effort and difficulty in detaching them, and consequently great confusion in the abstract idea; particularly as, from the restless nature of the mind, we cannot keep it an instant in one state, and consequently cannot steadily contemplate this idea; still, notwithstanding the ridicule which has been thrown on the doctrine from confounding it with the belief of abstract and real existences, it does appear that we have such things as abstract ideas though difficult to attain, momentary in their existence, and confused in their perception. Of course the more universal the conjunction of two states of mind has been, from the primary law of association, the more difficult it is to separate them and hence the extreme effort of separating the notion of colour from space, and of figure from extension. But that even this last is momentarily, and by an effort possible to the mind, may, I think be proved by an argument, which, though not metaphysical, or perhaps quite adapted to the nature of the subject, may perhaps be worth stating. It is quite certain that we should never be commanded by the Deity to perform a process which is impossible. But we are commanded by revelation to form a conception of the Deity invested with all the qualities which we find universally combined with figure, and extension, and colour, and yet to detach this conception from all such associations. The extreme difficulty of doing this has perhaps been the first cause of idolatry in all ages of the world and it is not the least beautiful contrivance in the scheme of Christianity, that all this difficulty should be avoided, without risking any of the innumerable mischiefs which flow from degrading the Deity into forms of our own imagination. With respect, however, to the whole doctrine of abstract ideas, we ought to remember that we very seldom have any ideas at all in our minds, distinct from external impressions, but those of words. It requires great concentration of thought, a total exclusion of external objects, strong previous affection of the organs, and an attention very painful and continued to call up any idea of the kind.--Words and sounds are the ideas which principally occupy our mind both sleeping and waking. And if we try to resuscitate distinctly the image of any object, however well known and strongly infixed in our memory, we shall soon be convinced of the difficulty of the task. Probably most of the beautiful creations of sculpture and painting have arisen from efforts of this kind-but they are neither natural, nor common, nor easy. : The perception of identity necessarily implies the recognition of an idea or succession of ideas now present in the mind, as having been previously present. It implies also a comparison between them and the notion appears to be acquired in this manner. Whenever the sight of an object has once called up in my mind a train of ideas, if, the next time I perceive one of these ideas externally, I find all the successive ones which I anticipate, satisfied and fulfilled, as I recognize the object by the anticipation of its qualities, I acknowledge its identity by finding those anticipations gratified.If, on entering a house, I anticipate a particular suite of rooms, furnished in a particular manner, and following in a certain succession; and connect these ideas with the idea of some other time and place not then present, I recognize them as a recurrence, not a first perception. And when I find them occur ring as I anticipated, I conceive the house which I am now in to be the same with the one which I was in before. When, however, any external object occurs to break the chain, I doubt its identity, and the more frequently this takes place, the more I hesitate. Hence the reason why the word sameness is used so vaguely-since it is difficult to say precisely how many recurring ideas must meet with a corresponding external impression to constitute that degree of similarity which we loosely denominate sameness, and the one more or less can scarcely be defined. One thing is evident, that we can never perceive two objects which produce precisely the same train of ideas in our minds, since there must always be a difference in point of time. The identity of an object is however determined by the uninterrupted succession of external impressions up to that point where our notion of the substantive ceases, and place or action is seldom if ever taken into consideration, except when two trains of ideas, the one present, the other repeated from a past perception, exactly correspond; and yet a difficulty arises in the mind at conceiving their identity, from the improbability of the object being transferred from one place to another, either at all or within a particular space of time; or from our not having watched connectedly its progress from one point to |