| A change in any considerable part of a body destroys its identity; but it is remarkable, that where the change is produced gradually and insensibly we are less apt to ascribe to it the same effect. |
| The reason can plainly be no other, than that the mind, in following the successive changes of the body, feels an easy passage from the surveying its condition in one moment to the viewing of it in another, and at no particular time perceives any interruption in its actions. |
| From which continued perception, it ascribes a continued existence and identity to the object. |
| But whatever precaution we may use in introducing the changes gradually, and making them proportionable to the whole, it is certain, that where the changes are at last observed to become considerable, we make a scruple of ascribing identity to such different objects. |
| There is, however, another artifice, by which we may induce the imagination to advance a step farther; and that is, by producing a reference of the parts to each other, and a combination to some common end or purpose. |
| A ship, of which a considerable part has been changed by frequent reparations, is still considered as the same; nor does the difference of the materials hinder us from ascribing an identity to it. |
| The common end, in which the parts conspire, is the same under all their variations, and affords an easy transition of the imagination from one situation of the body to another. |
| 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 phaenomena, 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 bears a noise, that is frequently interrupted and renewed, says, it is still the same noise; though it is 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 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 free-stone, 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. |