Popular Use.—There is a popular use of this term which requires further notice. We speak of the identity of a mountain, a river, a tree, or any like object in nature. It is the same mountain, we say, that we looked upon in childhood, the same tree under which we sat when a boy, the same river in which we bathed or fished in youth. Now there is a sense in which this is true and correct. There has been change of substance unquestionably, and therefore there is not absolute identity; but there is, after all, numerical sameness, and this is what we mean when we speak of the sameness or identity of the object. It constitutes a sufficient ground for such use of terms. You recognize the book, the mountain, the river, as one you have seen before. The tree that you pass in your morning walk you recognize as the very tree under which you sat ten years ago. Leaves have changed, bark and fibres have changed; branches are larger and more numerous; boughs, perhaps, have fallen by time and by tempest; it has changed as you have changed, it has grown old like yourself, with changing seasons; its verdure and foliage, like your hopes and plans, lie scattered around it, and yet it is to you the same tree. How so? It is the same numerical unity. Of a thousand or ten thousand similar trees, similar in species, in growth, and form, and adaptation of parts, in size, color, general appearance, etc., it is this individual one, and not some other of the same sort or species growing elsewhere, that you refer to. It is the same numerical unity and not some other one of the series. Still there must be continuity of existence in order to identity even in this popular sense of the term. Were the parts entirely changed and new ones substituted, as in the puzzle of the knife with several successive handles and blades, or the ship whose original timbers, planks, cordage, and entire substance, had, in course of time, by continued repairs, been removed and replaced by new; in such a case, we do not ordinarily speak or think of the object as being any longer the same.
This not absolute Identity.—In the cases now under consideration, in which, in popular language, objects are termed "same" and "identical," which are not strictly so, there is comparative rather than absolute unity and identity. There is reference always in such cases to other objects of the same kind, sort, and description, a series of which the object of present cognition is one, and to which series it holds the same relation now that it held formerly. As when, of several books on a table, you touch one, and after the interval of some moments or hours touch the same again; you say, The book I last touched is the same I touched before, the identical one; you do not mean that its substance is absolutely unchanged, that it has the same precise number of particles in its composition as before—this is not in your mind at all—but only that the unity thus designated is the same unity previously designated, that, and not some other one of the series of similar objects. It is a comparative idea, a comparative identity, in which numerical unity is the element chiefly regarded.
Possible Plurality implied.—In all cases where the idea of identity arises in the mind, there is implied a possible plurality of objects of the same general character; the idea of such diversity or plurality is before the mind, and the foundation of that idea is the difference of cognition. The same object is viewed by the same person at different times or by different persons at the same time, and in that case, though the object itself should be absolutely one and the same, yet there have been distinct, separate cognitions of it, and this plurality or difference of cognition is a sufficient foundation for the idea of a possible diversity of object. The book as known to-day and the book as known yesterday, are two distinct objects of thought. The cognition now, and the cognition then, are two separate acts of the mind; and the question arises, Are the objects distinct, as well as the cognitions? This is the question of identity. You have an immediate, irresistible conviction that the object of these several cognitions is one and the same. You affirm its identity, absolute or comparative, as the case may be.
The Conception of Identity amounts to what.—In every case of affirmed identity, then, there is implied a possible plurality of objects; a difference of cognition of a given object, whether one person cognizant at different times, or different persons at the same time; a question whether the possible plurality, as regards the object of these different cognitions, is an actual plurality; a conviction and decision that it is not, that the object is one and the same; and this sameness and unity are absolute or comparative, according as we use the language in its strict, primitive, philosophical meaning, or in its loose and popular sense. In the one case, it is sameness of absolute essence, in the other, sameness of nominal relation to others of a series or class.
IV. Cause.
Meaning of the Term.—The idea of cause is one with which every mind is familiar. It is not easy, however, to explain precisely what we mean by it, nor to fix its limits, nor to unfold its origin.
We mean by this term, I think, as ordinarily employed, that on which some consequence depends, that but for which some event or phenomenon would not occur. In order to affirm that one thing is the cause of another, I must know, not merely that they are connected, but that the existence of the one depends on that of the other. This is more than mere antecedence, however invariable. The approach of a storm may be invariably indicated by the changes of the barometer. These changes precede the storm, but are not the cause of it.
Origin of the Idea.—Whence do we derive the idea of cause?—a question of some importance, and much discussed.
Evidently not from sense. I observe, for example, the melting of snow before the fire, or wax before the flame of a taper. What is it that I see in this case? Merely the phenomenon, nothing more. All that sense conveys, all that the eye reports, is simply the melting of the one substance in the presence and vicinity of the other. I see no cause, no form transmitted from the one to the other, no action of the one on the other, but simply the vicinity of the two, and the change taking place in one. I infer that the change takes place in consequence of the vicinity. I believe it; and if the experiment is often repeated with the same results, I cannot doubt that it is so. The idea of causality is, indeed, suggested by what I have seen, but is not given by sense. I have not seen the cause; that lies hidden, occult, its nature wholly unknown, and its very existence known, not by what I have actually seen, but by that law of the mind which leads me to believe that every event must have a cause, and to look for that cause in whatever circumstance is known to be invariably connected with the given change or event.
Constitution of the Mind.—That such is the constitution of the mind, such the law of its action, admits of no reasonable doubt. No sooner is an event or phenomenon observed, than we conclude, at once, that it is an effect, and begin to inquire the cause. We cannot, by any effort of conception, persuade ourselves that there is absolutely no cause.