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 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.