Marsilio Ficino’s Platonic Theology, Volume II

3This is impious, because if bodies and souls were mutually transmuted, then all the more would any souls be transmuted into any other souls, and in turn any bodies into any other bodies. Let soul therefore be form alone—form, I say, not accidental but substantial. For since the soul itself is the ruler and mover of the body, containing it, holding it firm, and turning it, the soul is more excellent than the body. Body is a substance, and no accident is nobler than substance. Again, a mover, insofar as it is the principle of motion, does not depend for its being on what is moved. The soul itself, therefore, which is truly the mover of the body, does not depend upon the body as though it were the body's handmaid. It is consequently not an accident of body. Moreover, whatever receives opposites in turn while itself remaining the same is a substance. The soul, while remaining the same, receives now one opinion and now another opposed to it, now knowledge and now ignorance, as well as conflicting affections.

4The soul, then, is a substance—a substance, I say, as a certain substantial form. Form is not body, since every body is designated by some form; but form, insofar as it is form, cannot itself be formed. Hence soul is not a body. For the present I pass over the arguments showing that our soul cannot be an accident: if it inhered in a subject by some necessity, it could not resist that subject; it would never turn back upon itself; it would not rise above the kind of accidents to the kind of substance; nor could it properly define substance itself, distinguish it from accidents, or rightly measure how far it surpasses them.