Marsilio Ficino’s Platonic Theology, Volume II

8The same result will follow if the soul is a quality and a certain temperament of the humors and members. For quality flows away just as humor does. In the very process of nourishment the soul will flow out and flow back in like the body, and the animal will no more remain constant in its form than in its proper matter. Nor will the animal's unity beyond number be preserved, nor the continuity of the motion of nourishment or growth. Nor will there be in the animal any power that orders these motions, remaining so constant in itself that it both establishes the order in which they proceed and sets a limit to their progress—how long the animal ought to be nourished or to grow. The ruler that orders and brings moving things to rest must itself stand firm within itself.

9Someone may perhaps object: we see the same figure remain in our body for a very long time, although the flesh ebbs and flows. What, then, similarly prevents the same images of things known from remaining in the soul, although the soul's substance changes from an old one into a new? We answer that not precisely the same figure remains, nor one entirely similar. Rather, as the former flesh repeatedly departs, its figure departs with it, and in the fresh flesh a new figure is fashioned that in some measure resembles the former. This is done by a supremely stable craftsman working within. Because it always remains the same and contains within itself the patterns and seeds for arranging the members of its familiar body, it can give the new humors that flow in each day a temperament like the former one and can give the fresh flesh a figure like the old.

10It is just as a face, looking down upon a river from above, paints the flowing waves—new at every moment—with ever new images of itself, so that the same face appears to persist in the changing waters. That inward and stable craftsman of the body is the soul. If the soul itself also flows, the body will certainly not long display similar likenesses and forms, nor will the soul retain similar knowledge. For then the soul will not hold them by its own power, and no one will be present either to establish them firmly in the soul or to generate others like those that came before.