De causis curatricibus Theses Progymnasticae

XLIII.
Therefore, not just any power of the Soul, but—according to Aristotle, and indeed according to Galen and the Platonists—that which is a species, part, or faculty of the soul, accomplishes and performs what has been stated: specifically, that which is inferior to them, and which man shares with plants and animals, called Nature or the vegetative soul.

XLIV.
Elsewhere, however, Galen understands by "Nature" not the soul or the faculty that governs our body, but something else entirely; indeed, he explains it in various ways.

XLV.
He calls the temperament and the innate heat of the solid or spermatic parts "Nature," and he establishes these essences as the makers and effectors of actions. For in On Temperaments 3, he says Nature is the temperament or temperature of the four elements; but in book 12 of Methodus, he says Nature consists of three parts: spirit, solids, and fleshy substance. In his commentary on Aphorism 15, book 1, he says: "For there are three things of our own Nature or Temperament which have completed the substance: spirit, blood, and seminal moisture, from which the more solid parts of the animal are made at the first origin, and soon the growth in them is perfected." The same author shortly after: "Nature makes innate heat." For he says that "it did not fashion anything else in the animal from the beginning, just as it neither increased it again, nor nourished it up to death, except for this innate heat." Since this is the cause of natural works, etc.; for there is nothing else in the nature of animals besides this heat, according to the opinion of Hippocrates.

XLVI.
But in truth, these statements by philosophers and physicians are not at all contrary, however much they might exhibit a certain appearance of it at first glance. For there is some diversity only in the mode of consideration. Indeed, the consideration of the philosophers is a bit more general and broader, while that of the physicians is more narrow and restricted. The philosopher's consideration progresses toward the principal efficient causes, whereas the physician's consideration stays almost entirely with the more proximate ones, which are more manifest to the senses: a point which may now be explained a little more fully.

XLVII.
The Peripatetic philosophers, since there cannot be several forms of one matter (for otherwise there would be two composites at once), and since only one thing is substantiated by one form, and since the Form of man is the Soul, they establish only one Soul in him, and they do not tear it into parts, but say it is simple and indivisible by any parts.

XLVIII.
Aristotle does seem to concede different parts of the soul, such as when he says in 1 On the Parts of Animals: "But not every soul is the principle of motion, nor are all its parts. Rather, that which is in plants is for augmentation, but that which is sensitive is for alteration. Motion through place is something else, and not intellectual. For motion through place is present in other animals, but intellect in none. It is therefore clear that one should not speak of every soul in this way: