On the Making of Man by Gregory of Nyssa — Read

Now, if some things in creation possess the nutritive faculty, and others again are regulated by the perceptive faculty, while the former have no share of perception nor the latter of the intellectual nature, and if for this reason anyone is inclined to the opinion of a plurality of souls, such a man will be positing a variety of souls in a way not in accordance with their distinguishing definition. For everything which we conceive among existing things, if it be perfectly that which it is, is also properly called by the name it bears: but of that which is not every respect what it is called, the appellation also is vain. For instance: -- if one were to show us true bread, we say that he properly applies the name to the subject: but if one were to show us instead that which had been made of stone to resemble the natural bread, which had the same shape, and equal size, and similarity of colour, so as in most points to be the same with its prototype, but which yet lacks the power of being food, on this account we say that the stone receives the name of "bread," not properly, but by a misnomer, and all things which fall under the same description, which are not absolutely what they are called, have their name from a misuse of terms.

Thus, as the soul finds its perfection in that which is intellectual and rational, everything that is not so may indeed share the name of "soul," but is not really soul, but a certain vital energy associated with the appellation of "soul. " And for this reason also He Who gave laws on every matter, gave the animal nature likewise, as not far removed from this vegetative life, for the use of man, to be for those who partake of it instead of herbs: -- for He says, "Ye shall eat all kinds of flesh even as the green herb; " for the perceptive energy seems to have but a slight advantage over that which is nourished and grows without it. Let this teach carnal men not to bind their intellect closely to the phenomena of sense, but rather to busy themselves with their spiritual advantages, as the true soul is found in these, while sense has equal power also among the brute creation.