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Of Duration, and its simple Modes
§ 1. THERE is another sort of Distance, or Length, the Idea whereof we get not from the permanent parts of Space, but from the fleeting and perpetually perishing parts of Succession. This we call Duration, the simple Modes whereof are any different lengths of it, whereof we have distinct Ideas, as Hours, Days, Years, etc. Time, and Eternity.
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§ 3. 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. ’Tis 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 [198]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 our selves, or any thing else, Commensurate to the succession of any Ideas in our Minds, the Duration of our selves, or any such other thing co-existent with our Thinking.
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§ 5. Indeed a Man having from reflecting on the Succession and Number of his own Thoughts, got the Notion or Idea of Duration, he can apply that Notion to things, which exist while he does not think […]. And therefore, though a Man has no Perception of the length of Duration, which past whilst he slept or thought not: yet having observed the Revolution of Days and Nights, and found the length of their Duration to be in Appearance regular and constant, he can, upon the supposition, that that Revolution has proceeded after the same manner, whilst he was asleep or thought not, as it used to do at other times, he can, I say, imagine and make allowance for the length of Duration, whilst he slept. […]
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§ 9. […] There seem to be certain Bounds to the quickness and slowness of the Succession of those Ideas one to another in our Minds, beyond which they can neither delay nor hasten.
§ 10. The Reason I have for this odd conjecture is, from observing that in the Impressions made upon any of our Senses, [200]we can but to a certain degree perceive any Succession; which if exceeding quick, the Sense of Succession is lost, even in Cases where it is evident, that there is a real Succession. […] Such a part of Duration […], wherein we perceive no Succession, is that which we may call an Instant; and is that which takes up the time of only one Idea in our Minds, without the Succession of another, wherein therefore we perceive no Succession at all.
§ 11. This also happens, where the Motion is so slow, as not to supply a constant train of fresh Ideas to the Senses […]; and the Body, though it really moves, yet not changing perceivable distance with some other Bodies, […] seems to stand still, as is evident in the Hands of Clocks, and Shadows of Sun-dials, and other constant, but slow Motions, where though after certain Intervals, we perceive by the change of distance, that it hath moved, yet the Motion it self we perceive not.
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§ 17. Having […] got the Idea of Duration, the next thing natural for the Mind to do, is to get some measure of this common Duration, whereby it might judge of its different lengths, and consider the distinct Order, wherein several things exist, without which a great part of our Knowledge would be confused, and a great part of History be rendered very useless. This Consideration of Duration, as set out by certain Periods, and marked by certain Measures or Epochs, is that, I think, which most properly we call Time.
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[202]§ 19. The diurnal, and annual Revolutions of the Sun, as having been from the beginning of Nature, constant, regular, and universally observable by all Mankind, and supposed equal to one another, have been with Reason made use of for the measure of Duration. But the distinction of Days and Years, having depended on the motion of the Sun, it has brought this mistake with it, that it has been thought, that Motion and Duration were the measure one of another. […] whereas any constant periodical Appearance, or Alteration of Ideas in seemingly equidistant Spaces of Duration, if constant and universally observable, would have as well distinguished the intervals of Time, as those that have been made use of. For supposing the Sun, which some have taken to be a Fire, had been lighted up at the same distance of time that it now every Day comes about to the same Meridian, and then gone out again about twelve hours after, and that in the Space of an annual Revolution, it had sensibly increased in Brightness and Heat, and so decreased again; would not such regular Appearances serve to measure out the distances of Duration to all that could observe it, as well without as with Motion? For if the Appearances were constant, universally observable, and in equidistant Periods, they would serve Mankind for measure of time as well, were the Motion away.
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§ 21. […] We must […] carefully distinguish betwixt Duration it self, and the measures we make use of to judge of its length. Duration in it self is to be considered, as going on in one constant, equal, uniform Course: but none of the measures of it, which we make use of, can be known to do so; nor [204]can we be assured, that their assigned Parts or Periods are equal in Duration one to another; for two successive lengths of Duration, however measured, can never be demonstrated to be equal. The Motion of the Sun, which the World used so long, and so confidently for an exact measure of Duration, has, as I said, been found in its several parts unequal: and though Men have of late made use of a Pendulum, as a more steady and regular Motion, than that of the Sun or (to speak more truly) of the Earth; yet if any one should be asked how he certainly knows, that the two successive swings of a Pendulum are equal, it would be very hard to satisfie himself, that they are infallibly so: since we cannot be sure, that the Cause of that Motion which is unknown to us, shall always operate equally; and we are sure, that the Medium in which the Pendulum moves, is not constantly the same: either of which varying, may alter the Equality of such Periods, and thereby destroy the certainty and exactness of the measure by Motion, as well as any other Periods of other Appearances, the Notion of Duration still remaining clear, though our measures of it cannot any of them be demonstrated to be exact. Since then no two Portions of Succession can be brought together, it is impossible ever certainly to know their Equality. All that we can do for a measure of Time, is to take such as have continual successive Appearances at seemingly equidistant Periods; of which seeming Equality, we have no other measure, but such as the train of our own Ideas have lodged in our Memories, with the concurrence of other probable Reasons, to perswade us of their Equality.
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