Plutarch, De animae procreatione in Timaeo
Goodwin, Ed.

All these philosophers likewise equally hold that the soul neither derives its beginning from time nor is the product of generation, but that it is endued with several faculties and virtues, into which Plato, as it were, melting and dissolving its substance for contemplation's sake, supposes it in his discourse to have had its original from procreation and mixture.

The same was his opinion concerning the world; for he knew it to be uncreated and without end, but not perceiving it so easy to apprehend how the structure was reared, or by what order and government supported, unless by admitting its beginning and the causes thereto concurring, he followed that method to instruct himself. These things being thus generally by them laid down, Eudorus will allow to neither side any share of probability; and indeed to me they both seem to have wandered from the opinion of Plato, if we intend to make the most likely rule our [p. 329] guide,—which is not to advance our own conceits, but to come as close as we can to his sense and meaning. Now as to this same mixture (as they call it) of the intelligible and sensitive substance, no reason appears why it should be more the original of the soul than of any other thing that ye can name. For the whole world itself and every one of its parts pretend to no other composition than of a sensitive and an intelligible substance, of which the one affords matter and foundation, the other form and figure to the whole mass. And then again, whate'er there is of material substance, framed and structured by participation and assimilation of the intelligible nature is not only to be felt but visible to the eye; whenas the soul still soars above the reach of all natural apprehension. Neither did Plato ever assert the soul to be number, but a perpetually self-moving nature, the fountain and principle of motion. Only he embellished and adorned the substance of it with number, proportion, and harmony; as being a subject capable of receiving the most goodly form which those ornaments could produce. So that I cannot believe it to be the same thing to compose the soul according to number, and to affirm the soul to be number itself. Nor can it be said to be harmony because harmoniously composed, as he has clearly demonstrated in his Treatise of the Soul. But plain it is, that those philosophers understood not the meaning of the Same and the Other. For they tell us how the Same contributes rest, the Other motion toward the generation of the soul. Though Plato himself, in his treatise entitled the Sophist, disposes and distinguishes Essence, the Same, the Other, together with Motion and Rest, as being five things altogether differing one from another and void of mutual affinity.