The thing here considered, and as I think, demonstratively determined, is proposed by Mr. Locke in these words, _Whether it_; _i.e._ the same self or person, _be the same identical substance_? And he has suggested what is a much better answer to the question, than that which he gives it in form. For he defines person, _a thinking intelligent being_, &c., and personal identity, _the sameness of a rational being_.[301] The question then is, whether the same rational being is the same substance: which needs no answer, because being and substance, in this place, stand for the same idea. The ground of the doubt, whether the same person be the same substance, is said to be this; that the consciousness of our own existence, in youth and in old age, or in any two joint successive moments, is not the _same individual action_,[302] _i.e._ not the same consciousness, but different successive consciousnesses. Now it is strange that this should have occasioned such perplexities. For it is surely conceivable, that a person may have a capacity of knowing some object or other to be the same now, which it was when he contemplated it formerly: yet in this case, where, by the supposition, the object is perceived to be the same, the perception of it in any two moments cannot be one and the same perception. And thus, though the successive consciousnesses, which we have of our own existence, are not the same, yet are they consciousnesses of one and the same thing or object; of the same person, self, or living agent. The person, of whose existence the consciousness is felt now, and was felt an hour or a year ago, is discerned to be; not two persons, but one and the same person; and therefore is one and the same.