Whether we are to live in a future state, as it is the most important question which can possibly be asked, so it is the most intelligible one which can be expressed in language. Yet strange perplexities have been raised about the meaning of that identity or sameness of person, which is implied in the notion of our living now and hereafter, or in any two successive moments. And the solution of these difficulties hath been stranger than the difficulties themselves. For, personal identity has been explained so by some, as to render the inquiry concerning a future life of no consequence at all to us the persons who are making it. And though few men can be misled by such subtleties; yet it may be proper to consider them a little. When it is asked _wherein_ personal identity consists, the answer should be the same, as if it were asked wherein consists similitude, or equality; that all attempts to define would but perplex it. Yet there is no difficulty at all in ascertaining _the idea_. For as, upon two triangles being compared or viewed together, there arises to the mind the idea of similitude; or upon twice two and four, the idea of equality: so likewise, upon comparing the consciousness of one’s self, or one’s own existence, in any two moments, there as immediately arises to the mind the idea of personal identity. And as the two former comparisons not only give us the ideas of similitude and equality; but also show us that two triangles are alike, and twice two and four are equal: so the latter comparison not only gives us the idea of personal identity, but also shows us the identity of ourselves in those two moments; the present, suppose, and that immediately past; or the present, and that a month, a year, or twenty years past. In other words, by reflecting upon that which is myself now, and that which was myself twenty years ago, I discern they are not two, but one and the same self. But though consciousness of what is past does thus ascertain our personal identity to ourselves, yet to say, that it _makes_ personal identity, or is necessary to our being the same persons, is to say, that a person has not existed a single moment, nor done one action, but what he can remember; indeed none but what he reflects upon. And one should really think it self-evident, that consciousness of personal identity presupposes, and therefore cannot constitute, personal identity; any more than knowledge, in any other case, can constitute truth, which it presupposes.