Marsilio Ficino’s Platonic Theology, Volume II

4When the soul is moved in its own manner, it does not scatter the body, for the soul's motion through the body causes no pain. Yet pain would arise continually in the body if its parts were scattered and disturbed by the soul's motion. They would certainly be scattered if the soul were a body, since the soul itself moves perpetually through the body with a motion of its own. How, then, could the soul be a body when it is everywhere throughout the body and, without injuring it in any way, fills and penetrates the whole from every side? Moreover, if the soul were a solid body, either it would not fill the whole body, and the whole would therefore not live, or, if it did fill it, the soul would break the body by penetrating it and would itself be broken, and continual pain would arise in us. If instead it were a fluid and unstable body, the soul would neither bind nor firmly consolidate the animal's body; rather, as we said above, it too would need some other bond by whose stability it might be held firm, governed, and moved. We should more readily call that bond the soul—or rather the soul's power. For the soul's power in the body is much like the power of rennet in milk, which it curdles; the power of a magnet in iron, which it draws and suspends; or the ordering skill in a clock, by which the clock is governed, moved, and made to sound in marvelous order. The soul itself, however, is not a power or a tempering of the humors, but a substantial form—simple and indivisible—which by its natural power and art tempers the spirits, humors, and members.