Chapter 076 - The Union of Soul and Body

The intellect, which is the principle of intellectual operation, is the form of the human body; for that which is the principle by which anything operates is the form of the thing to which the operation is attributed. It is also evident that where the body lives, there the soul is; and this life is manifested in living beings in various degrees according to its different operations; for by the soul we are nourished, feel and move. Therefore that by which we understand, whether it be called the intellect or the intellectual soul, is the form of the body. For the nature of a thing is manifested by its operation, and understanding is the operation proper to man; since it is by this that he transcends all other animals.

To the arguments of Averroes, who maintained that the soul was united to the body as motor, we reply, that by such a union man would not understand, but be understood by a soul capable of existing in a state of separation. Moreover, if the intellectual principle be not the form of the man, it must be extrinsic to his substance; but the act of understanding is not transmitted; it rests in him who understands.

It is likewise impossible that the intellect by which we understand should be the same in all; for granting the soul to be the man, it would follow that Socrates and Plato were identical, without any distinction except that of tunic and cloak; besides, if there were one intellect for all, all men would have the same conception of the object understood; which things are absurd. There is not, therefore, one intellect for all.

Nor are there other souls in man differing in essence from the intellectual soul; the nutritive, sensitive, and intellectual soul is one and the same. This may be seen by noting the differences of species and forms according to their degrees of perfection; comparing animals with plants, and man with animals. Aristotle^ compares different souls to figures, one of which contains the other, as a pentagon contains a quadrangle: thus the intellectual soul contains virtually all that belongs to the sensitive faculties of the lower animals and to the nutritive life of plants. Nor is Socrates a man by one soul and an animal by another; as the surface which bears the figure of a pentagon is not one for the pentagon and another for the quadrangle.

Reason also tells us that the soul is one. For an animal would not be really one if it had several souls; nor is anything absolutely one except in virtue of the one form by which it has being, and by which it both is, and is at the same time, one. The unity of the soul is apparent, also, from the fact that one mental operation, if it be intense, hinders another; which could by no means occur unless the principle of action were essentially the same. Therefore the soul is one: it alone is the substantial form in man; and contains virtually both the sensitive and nutritive faculties; and by itself alone supplies whatever less perfect forms operate in others, viz. the sensitive soul in the lower animals, and the nutritive soul in plants. And the same holds good of all the more perfect forms in respect of the less perfect. Moreover, if any other form pre-existed, the soul would not give being absolutely, and so would not be a substantial form; neither would generation depend absolutely upon its advent; which is evidently false.

It is necessary that the body to which an intellectual soul is united should be mixed, i.e. composed of diverse elements perfectly reduced to harmony. For Nature does not fail to produce what is necessary, and the human soul being weak among intellectual beings, and not having infused knowledge like the angels, requires faculties of understanding and feeling which do not exist without bodily organs: therefore, as the intellectual soul possesses sensitive faculties in the highest perfection, it was necessary that this compound body should be brought into perfect harmony of constitution. Thus man, among all animals, has the finest sense of touch; and those persons who have the finest touch have also the finest intelligence; for, according to Aristotle, soft flesh is well adapted to mind.

No accidental dispositions conduce towards the union of the intellectual soul with the body; for matter in potentia bears relation to all actuality. Therefore what is first actualized must be understood as existing in matter. But first among actualities is being, since a thing must exist before it can be hot or cold; hence it is impossible that accidental dispositions should pre-exist in matter before the substantial form, as though the soul were united as motor to the body.

Nor can the soul be united to the body through the medium of any other body. For form, of itself, constitutes a thing in actual being; nor does it give being by means of any medium, because it is actuality by its essence. Those are in error, therefore, who hold some body to be the medium between the soul and the body in man: as Plato, who taught that the soul was united to the body as motor, so that media might be admitted to intervene.

And being united to the body as form, the soul must of necessity be entire in the whole body, and entire in every part; because a substantial form is the perfection, not merely of the whole, but of every part. Hence, when the soul has departed, we can no longer speak of a man, or of an animal, except equivocally; and the same may be said of a hand or an eye. The proof of this is that no part of the body can perform the work proper to it when the soul is gone; for that which retains the species, retains also the operation of the species. So the soul, according to the threefold division of totality,^ has no quantity, either in itself or accidentally, but is entire in the whole body and entire in every part according to the totality of perfection and essence; but not according to that of power; for the soul is not in every part of the body according to all its faculties; but as regards sight it is in the eye, hearing in the ear, and so on.