Marsilio Ficino’s Platonic Theology, Volume II

8Forms that remain in themselves, however, and only seem at times to inhere in matter, sustain matter rather than being sustained by it. They cannot admit a force contrary to themselves. If such a force enters matter’s womb, it stains the qualities and forms bound to matter, but it does not touch the form that rises above matter. Such is the soul—the rational soul, I mean. Since it is the fountain of motion and the mover of bodies, bodies cannot dislodge it from its state. And because it possesses as its own a life inborn in its species, it lives forever without the labor of living, above all while it lives with itself. Yet as it approaches body, it pours from itself, to speak as a Platonist, an irrational life like a shadow. The rational soul itself is true soul and the fountain of animal life. It supplies such life not only to the body for a time but, far more, to itself forever, since it never deserts itself and cannot be compelled to do so by body, whose quality does not pass into incorporeal form. Nor can it be forced to this by other souls, whose office is to give life, not to destroy. Such, beyond doubt, is the rational soul. The irrational soul, by contrast, is not true soul, because it is neither true essence nor true life. It is not true essence because it does not exist through itself: it does not act through itself, since it does nothing without bodily instruments. It is not true life because it lacks freedom of motion; it is not led by itself but forcibly drawn by objects presented to the senses. Hence many Platonists say that the rational soul is both soul and subsistent life and gives life to the body from itself; but they regard the irrational soul rather as a form—the animation and vivification of the body. Xenocrates, Speusippus, Numenius, and Plotinus hold that this irrational soul too is immortal; Porphyry, Proclus, and very many others deny it. We should not be surprised that many Platonists call some souls true and others false, for the variety of things is joined together by fitting intervals.