Proclus: Commentary on Plato's Timaeus, Vol. I

So it is necessary for that which is to be likened more to the intelligible to have some sort of eternity, and for that which is eternal, yet does not have eternity present with it all at once, as the intelligible possesses it entirely, to have time as its whole. However, if one were to examine the nature of time, one will know more clearly how time contributes not only to eternity for the whole cosmos and the great parts of the cosmos, but also how it assists in perfection and happiness for each of them and for all together. This, as the exposition proceeds, we too will attempt to reveal by investigating the completions regarding time.

"The nature of the animal, therefore, happened to be eternal, and it was not possible to attach this to the generated being entirely. But he devised to make a certain moving eikon image of eternity, and while ordering the heavens, he makes an eternal image of that which remains in eternity, moving according to number, which indeed we have named time" [37D].

That the autozōon Self-Animal is a completion of the multitude of intelligible animals and that it always exists in the same way and in the same manner is one of those things which has been often contemplated and pressed, and which has admitted no dispute among the philosophers from Plato. But what eternity is, and what time is that imitates it in a moving manner, this is very difficult both to conceive and to interpret in a firm manner. Nevertheless, one must speak about both in the most elegant way possible according to the views of the elders, and if we might be able to add anything contributing to the clarity and articulation of the subjects proposed for investigation. Now, the conception and sense-perception of time are possessed by the majority of people, looking toward the motion of the things beneath the moon and the motion of the heavenly bodies, and considering time to be some sort of movement.