Enneads III.7: Of Time and Eternity
Polemic Against the Pythagoreans: Time Is Not What Is Movable
On the other hand, if time be not the movement of the sphere, evidently it is far less (than that which is movable, as thought the Pythagoreans,[449]) or (as Pythagoras thought), the sphere (of heaven) itself, as some have thought, because it moves. (This fact alone is sufficient to refute the opinion that confuses time with that which is movable).
POLEMIC AGAINST THE STOIC ZENO: TIME IS NO INTERVAL OF MOVEMENT.
Is time then some part of movement? (Zeno[450]) calls it the interval of movement; but the interval is not the same for all movements, even if the latter were of similar nature; for movements that operate within space may be swifter or slower. It is possible that the intervals of the most rapid and of the slowest movement might be measured by some third interval, which might far more reasonably be considered time. But which of these three intervals shall be called time? Rather, which of all the intervals, infinite in number as they are, shall time be? If time be considered the interval of the regular movement, it will not be the particular interval of every regular movement; otherwise, as there are several regular movements, there would be several kinds of time. If time be defined as the interval of movement of the universe, that is, the interval contained within this movement, it will be nothing else than this movement itself.
PERSISTENT MOVEMENT AND ITS INTERVAL ARE NOT TIME, BUT ARE WITHIN IT.
Besides, this movement is a definite quantity. Either this quantity will be measured by the extension of the space traversed, and the interval will consist in that extension; but that extension is space, and not time. Or we shall say that movement has a certain interval because it is continuous, and that instead of stopping immediately it always becomes prolonged; but this continuity is nothing else than the magnitude (that is, the duration) of the movement. Even though after consideration of a movement it be estimated as great, as might be said of a "great heat"--this does not yet furnish anything in which time might appear and manifest; we have here only a sequence of movements which succeed one another like waves, and only the observed interval between them; now the sequence of movements forms a number, such as two or three; and the interval is an extension. Thus the magnitude of the movement will be a number, say, such as ten; or an interval that manifests in the extension traversed by the movement. Now the notion of time is not revealed herein, but we find only a quantity that is produced within time. Otherwise, time, instead of being everywhere, will exist only in the movement as an attribute in a substrate, which amounts to saying that time is movement; for the interval (of the movement) is not outside of movement, and is only a non-instantaneous movement. If then time be a non-instantaneous movement, just as we often say that some particular instantaneous fact occurs within time, we shall be forced to ask the difference between what is and what is not instantaneous. Do these things differ in relation to time? Then the persisting movement and its interval are not time, but within time.