2.  Its Idea from Reflection on the Train of our Ideas.

The answer of a great man, to one who asked what time was:  Si non rogas intelligo, (which amounts to this; The more I set myself to think of it, the less I understand it,) might perhaps persuade one that time, which reveals all other things, is itself not to be discovered.  Duration, time, and eternity, are, not without reason, thought to have something very abstruse in their nature.  But however remote these may seem from our comprehension, yet if we trace them right to their originals, I doubt not but one of those sources of all our knowledge, viz. sensation and reflection, will be able to furnish us with these ideas, as clear and distinct as many others which are thought much less obscure; and we shall find that the idea of eternity itself is derived from the same common original with the rest of our ideas.

3.  Nature and origin of the idea of Duration.

To understand time and eternity aright, we ought with attention to consider what idea it is we have of duration, and how we came by it.  It is evident to any one who will but observe what passes in his own mind, that there is a train of ideas which constantly succeed one another in his understanding, as long as he is awake.  Reflection on these appearances of several ideas one after another in our minds, is that which furnishes us with the idea of succession:  and the distance between any parts of that succession, or between the appearance of any two ideas in our minds, is that we call duration.  For whilst we are thinking, or whilst we receive successively several ideas in our minds, we know that we do exist; and so we call the existence, or the continuation of the existence of ourselves, or anything else, commensurate to the succession of any ideas in our minds, the duration of ourselves, or any such other thing co-existent with our thinking.

4.  Proof that its idea is got from reflection on the train of our ideas.

That we have our notion of succession and duration from this original, viz. from reflection on the train of ideas, which we find to appear one after another in our own minds, seems plain to me, in that we have no perception of duration but by considering the train of ideas that take their turns in our understandings.  When that succession of ideas ceases, our perception of duration ceases with it; which every one clearly experiments in himself, whilst he sleeps soundly, whether an hour or a day, a month or a year; of which duration of things, while he sleeps or thinks not, he has no perception at all, but it is quite lost to him; and the moment wherein he leaves off to think, till the moment he begins to think again, seems to him to have no distance.  And so I doubt not it would be to a waking man, if it were possible for him to keep only one idea in his mind, without variation and the succession of others.  And we see, that one who