Opposite of Diversity.—To affirm identity, then, is simply to deny diversity, to predicate unity, sameness, oneness. Other objects there are, like this, it may be, similar in every respect, capable of being confounded with it, and mistaken for it, but they are other and not it. This we affirm when we affirm identity, non-diversity, non-otherness. Whatever it be that marks off and distinguishes a thing from all other like or unlike objects—whatever constitutes its individuality, its essence—in that consists its identity.
Different applications of the Term.—Evidently, then, the word has somewhat different senses as applied to different classes of objects, whose individuality or essence varies. There are three distinct classes of objects to which the term is applicable. 1. Spiritual existence. 2. Organic and animate material existence. 3. Inorganic matter.
As applied to the first Class.—As regards the first class, spiritual existences, their identity consists in simple oneness and continuity of existence. It is enough that the soul or spirit exist, and continue to exist. So long as this is the case, identity is predicable of it. Should that existence cease, the identity ceases, since the object no longer exists of which identity can be affirmed. Should another spirit be created in its place, and even, if the thing be supposable, should it be endowed, not only with the same qualities, but the same consciousness, so as to be conscious of all that of which the former was conscious, still it would not be identical with the former. It is, by the very supposition, another spirit, and not the same. To be identical with it, it must be the very same essence, being, or existence, and not some other in its place.
It is only of spiritual immaterial existence that identity, in its strict and complete sense, is properly predicable, since it is only this class of existences that retains, unimpaired, its simple oneness, sameness, continuity of essence.
Personal Identity.—When we speak of personal identity, we mean that of the spirit, the soul, the ego, in distinction from the corporeal material part. The evidence of personal identity is consciousness. We know that the thinking conscious existence of to-day, which we call self, me, is one and the same with the thinking conscious self or me of yesterday, and not some other personal existence of like attributes and condition.
Locke's Idea.—Mr. Locke strangely mistook the evidence of personal identity for identity itself, and affirmed that our identity consists in our consciousness. If this were so, then, whenever our consciousness were interrupted, as in sound sleep, or in fainting, or delirium, our identity would be gone. This error has been pointed out, and fully explained, by Dr. Reid, and Bishop Butler, the former of whom makes this supposition: that the same individual is, at different periods of life, a boy at school, a private in the army, and a military commander; while a boy, he is whipped for robbing an orchard; when a soldier, he takes a standard from the enemy, and at that time recollects, perfectly, the whipping when a boy; when commander, he remembers taking the standard but not the whipping. It follows, according to Mr. Locke, that the soldier is identical with the boy, and the general with the soldier, because conscious of the same things, but the general is not identical with the boy, because not conscious of the same things, that is, a is b, and b is c, yet a is not c. The truth is, identity, and the evidence of it, are two things. Were there no consciousness of any thing past, there would still be identity so long as unity and continuity of existence remained.
2. Identity as applied to the second Class.—As regards organic material existence, whether animal or vegetable, the identity consists in that which constitutes the essence or being of the thing, which constitutes it an animal or vegetable existence. It is not mere body, not mere particles of matter, of such number and nature, or even of such arrangement and structure, but along with this, there is a higher principle involved—that of life. The continuity of this mysterious principle of life, under the same general structure and organization of material parts, making throughout one complex unity, one entity, one being, though with many changes, it may be, of separate parts and particles composing the organization; this constitutes the identity of the object.
The identity is no longer complete, no longer absolute, because there is no longer, as in the case of spiritual existence, absolute sameness of essence. Of the complex being under consideration, animal or vegetable, the life-principle is, indeed, one and the same throughout all periods of its existence, but the material organization retains not the same absolute essence, only the same general structure, and form, and adaptation of parts, while the parts and particles themselves are continually changing. It is only in a modified and partial sense, then, not in strict philosophical use of language, that we can predicate identity of any material organic existence. We mean by it, simply, continuity of life under the same general structure and organization; for so far as it has unity at all, this is it. This enables us to distinguish such an object from any and all other like objects of the same kind or sort.
3. Identity as applied to the third Class.—As regards mere inorganic matter, its identity consists, again, in its absolute oneness and sameness. There must be no change of particles, for the essence of the thing now considered lies not in any peculiarity of form, or structure, or life-principle, all which are wanting, but simply in the number and nature of the particles that make up the mass or substance of the thing, and if these change in the least, it is no longer the same essence. There is, properly, then, no such thing as identity in the cases now under consideration, since the particles of any material substance are liable to constant changes. It is only in a secondary and popular sense that we speak of the identity of merely inorganic material substance; strictly speaking, it has no identity, and continues not the same for any two moments.
We say, however, of two pieces of paper, that they are of the same color, meaning that they are both white or both red; of two coins, that they are of the same fineness, the same size, and weight, etc., meaning, thereby, only that the two things are of the same sort of color, the same degree of fineness, etc., and not that the color of the one or the fineness and size of the one is absolutely the essential and identical color, size, fineness of the other. It is by a similar use of terms, not in their strict and proper, but in a loose and secondary sense, that we speak of the identity or sameness of any material substance in itself considered. Strictly, it has no identity unless its substance is absolutely unchanged, which is not true of most, if, indeed, of any material existence, for any successive periods of time.