_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.