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But this is still more remarkable, when we add a sympathy of parts to their common end, and suppose that they bear to each other the reciprocal relation of cause and effect in all their actions and operations. This is the case with all animals and vegetables; where not only the several parts have a reference to some general purpose, but also a mutual dependence on, and connexion with, each other. The effect of so strong a relation is, that though every one must allow, that in a very few years both vegetables and animals endure a total change, yet we still attribute identity to them, while their form, size and substance, are entirely altered. An oak that grows from a small plant to a large tree is still the same oak, though there be not one particle of matter or figure of its parts the same. An infant becomes a man, and is sometimes fat, sometimes lean, without any change in his identity.
We may also consider the two following phenomena, which are remarkable in their kind. The first is, that though we commonly be able to distinguish pretty exactly betwixt numerical and specific identity, yet it sometimes happens that we confound them, and in our thinking and reasoning employ the one for the other. Thus, a man who hears a noise that is frequently interrupted and renewed, says it is still the same noise, though 'tis evident the sounds have only a specific identity or resemblance, and there is nothing numerically the same but the cause which produced them. In like[Pg 328] manner it may be said, without breach of the propriety of language, that such a church, which was formerly of brick, fell to ruin, and that the parish rebuilt the same church of freestone, and according to modern architecture. Here neither the form nor materials are the same, nor is there any thing common to the two objects but their relation to the inhabitants of the parish; and yet this alone is sufficient to make us denominate them the same. But we must observe, that in these cases the first object is in a manner annihilated before the second comes into existence; by which means, we are never presented, in any one point of time, with the idea of difference and multiplicity; and for that reason are less scrupulous in calling them the same.
Secondly, we may remark, that though, in a succession of related objects, it be in a manner requisite that the change of parts be not sudden nor entire, in order to preserve the identity, yet where the objects are in their nature changeable and inconstant, we admit of a more sudden transition than would otherwise be consistent with that relation. Thus, as the nature of a river consists in the motion and change of parts, though in less than four-and-twenty hours these be totally altered, this hinders not the river from continuing the same during several ages. What is natural and essential to any thing is, in a manner, expected; and what is expected makes less impression, and appears of less moment than what is unusual and extraordinary. A considerable change of the former kind seems really less to the imagination than the most trivial alteration of the latter; and by breaking less the continuity of the thought, has less influence in destroying the identity.
We now proceed to explain the nature of personal[Pg 329] identity, which has become so great a question in philosophy, especially of late years, in England, where all the abstruser sciences are studied with a peculiar ardour and application. And here 'tis evident the same method of reasoning must be continued which has so successfully explained the identity of plants, and animals, and ships, and houses, and of all the compounded and changeable productions either of art or nature. The identity which we ascribe to the mind of man is only a fictitious one, and of a like kind with that which we ascribe to vegetables and animal bodies. It cannot therefore have a different origin, but must proceed from a like operation of the imagination upon like objects.
But lest this argument should not convince the reader, though in my opinion perfectly decisive, let him weigh the following reasoning, which is still closer and more immediate. 'Tis evident that the identity which we attribute to the human mind, however perfect we may imagine it to be, is not able to run the several different perceptions into one, and make them lose their characters of distinction and difference, which are essential to them. 'Tis still true that every distinct perception which enters into the composition of the mind, is a distinct existence, and is different, and distinguishable, and separable from every other perception, either contemporary or successive. But as, notwithstanding this distinction and separability, we [suppose] the whole train of perceptions to be united by identity, a question naturally arises concerning this relation of identity, whether it be something that really binds our several perceptions together, or only associates their ideas in the imagination; that is, in other words, whether, in pronouncing concerning the identity[Pg 330] of a person, we observe some real bond among his perceptions, or only feel one among the ideas we form of them. This question we might easily decide, if we would recollect what has been already proved at large, that the understanding never observes any real connexion among objects, and that even the union of cause and effect, when strictly examined, resolves itself into a customary association of ideas. For from thence it evidently follows, that identity is nothing really belonging to these different perceptions, and uniting them together, but is merely a quality which we attribute to them, because of the union of their ideas in the imagination when we reflect upon them. Now, the only qualities which can give ideas an union in the imagination, are these three relations above mentioned. These are the uniting principles in the ideal world, and without them every distinct object is separable by the mind, and may be separately considered, and appears not to have any more connexion with any other object than if disjoined by the greatest difference and remoteness. 'Tis therefore on some of these three relations of resemblance, contiguity and causation, that identity depends; and as the very essence of these relations consists in their producing an easy transition of ideas, it follows, that our notions of personal identity proceed entirely from the smooth and uninterrupted progress of the thought along a train of connected ideas, according to the principles above explained.
The only question, therefore, which remains is, by what relations this uninterrupted progress of our thought is produced, when we consider the successive existence of a mind or thinking person. And here 'tis evident we must confine ourselves to resemblance and causation, and must drop contiguity, which has little or no influence in the present case.
To begin with resemblance; suppose we could see clearly into the breast of another, and observe that succession of perceptions which constitutes his mind or thinking principle, and suppose that he always preserves the memory of a considerable part of past perceptions, 'tis evident that nothing could more contribute to the bestowing a relation on this succession amidst all its variations. For what is the memory but a faculty, by which we raise up the images of past perceptions? And as an image necessarily resembles its object, must not the frequent placing of these resembling perceptions in the chain of thought, convey the imagination more easily from one link to another, and make the whole seem like the continuance of one object? In this particular, then, the memory not only discovers the identity, but also contributes to its production, by producing the relation of resemblance among the perceptions. The case is the same, whether we consider ourselves or others.
