De causis curatricibus Theses Progymnasticae

Nature, or Soul (for it signifies the same thing here), is in plants, as we just mentioned, vegetative; in animals, sensitive; and in humans, rational.

XXXVII.
I maintain that the Soul is that which moves, informs, nourishes, and grows the body; it keeps it healthy, cures it when ill, and protects its life and integrity. It is imbued with the art, powers, and modes of acting from the universal Nature, or (as philosophers speak elsewhere) the "Nature that natures" original: "Natura naturante", that is, God the supreme creator. Just as He created, preserves, and governs the whole universe, so He willed that it, as a kind of image of Himself, should not only be within the body but also rule over it.

XXXIIX.
That these things are so is confirmed not only by probable reasoning but also by the authority of the most learned men and wisest philosophers.

XXXIX.
For, to bring forward at least one or two examples from among infinite testimonies, Aristotle says in book 2 On the Soul: "The Soul is the ἐντελέχεια entelechy, or the first act and perfection of a natural organic body having life in potentiality." Likewise: "The Soul is that by which we primarily live, perceive, and understand." Plato and Proclus say that it is a property of the soul to be "a body possessing itself" original: "σῶμα τὸ αὐτῷ ἔχον". Galen, in his book Whether what is contained in the womb is an animal, says: "It is clear that, along with the seed cast into the womb, a soul is implanted by the Creator of the Universe, so that it might have the power of governing the body." Likewise, in his book On Natural Faculties: "The Nature of animals is the preserver, the finisher, and the judge of diseases; it preserves what is suitable and separates what is alien." Likewise, in his commentary on Hippocrates' On Popular Diseases, 5th commentary: "For Nature is that which does all things fittingly in the bodies of animals: it nourishes when there is need of food; it prepares blood for itself, through which it may nourish the particles lacking food; and so that the blood itself can be created, it prepares and perfects the food in the stomach." Thus, through these powers, it not only preserves the animal in health but also restores health to the sick.

XL.
However, philosophers and physicians do not define these things so crudely, simply, indiscriminately, or indeterminately without explaining their opinion more specifically, and it even seems that they disagree among themselves in certain ways.

XLI.
Aristotle posits a single soul in man (it is unnecessary to speak further of plants and animals) but asserts that it is endowed with several powers and forces: namely, the intellectual, the sensitive, and the natural, or vegetative or plant-like. He does not think that these powers are anything outside the essence of the soul; rather, he thinks they exist in the soul itself—indeed, that they are the soul itself.

XLII.
Galen, along with the Platonists, treats what Aristotle calls "powers" as species and parts, using the same names. He uses the term "faculty" elsewhere, but differently than Aristotle: namely, to understand faculty, part, and species of the soul as one and the same thing.