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.
