Summa contra Gentiles2.69 Chapter LXIX. Solution of the arguments by which it was proved above that an intellectual substance cannot be united to the body as its form

Taking the foregoing into consideration, it is not difficult to solve the arguments given above against the aforesaid union. In the first argument something false is taken for granted. Because body and soul are not two actually existing substances, but one actually existing substance is made from them: for man’s body is not actually the same 1 Ch. Ixviii. 2 Ch. Ivi.

while the soul is present, and when the soul is absent: and it is the soul that makes it to be actually.

The statement, contained in the second objection, that form and matter belong to the same genus, is true, not as though they were both species of the same genus, but because they are the principles of the same species. Accordingly, the intellectual substance and the body, which if they existed apart would be species of different genera, through being united are of the same genus as principles thereof.

Nor does it follow that the intellectual substance is a material form, although its being is in matter; as the third argument contended. For it is not in matter as merged in matter, or wholly encompassed by matter, but in another way, as stated.

Nor does the intellectual substance being united to the body as its form prevent the intellect being separate from the body, as the philosophers say. For we must consider in the soul, both its essence and its power. According to its essence it gives being to such and such a body, while according to its power it accomplishes its proper operations. If therefore an operation of the soul be accomplished by means of a corporeal organ, it follows that the power which is the principle of that operation, is the act of that part of the body by which its operation is accomplished: thus sight is the act of the eye. If, however, its operation be not accomplished by means of a corporeal organ, its power will not be the act of a body. It is in this sense that the intellect is said to be separate, and this does not preclude the substance of the soul of which the intellect is a power, otherwise the intellective soul, from being the act of the body, as the form which gives being to such a body.

And although the soul by its substance is the form of the body, it is not necessary that its every operation be performed by means of the body, and that consequently its every power be the act of a body, as the fifth argument supposed. For it has been already shown that the human soul is not such a form as is wholly merged in matter, but is of all other forms raised highest above matter. Consequently it can produce an operation without the body, as being independent of the body in operating: since not even in being does it depend on the body.

In the same way it is clear that the reasons whereby Averroes tries to confirm his opinion, do not prove that the intellectual substance is not united to the body as its form.

For the expressions used by Aristotle in reference to the possible intellect, when he says that it is impassible, unmixed, and separate, do not oblige us to admit that the intellective substance is not united to the body as the form whence the latter has being. For they are also true if we say that the intellective power, which Aristotle calls the power of understanding, is not the act of an organ, as though it exercised its operation thereby. This is in fact shown by his proof: since he proves that it is unshackled and separate, from its operation whereby it understands all things; and because operation belongs to a power as to its principle.

It is consequently clear that neither does Aristotle’s proof show that the intellective substance is not united to the body as its form. For if we suppose that the soul’s substance is thus united to the body in being, and that the intellect is not the act of any organ, it will not follow that the intellect has a particular nature,—I refer to the natures of sensibles: since it is not admitted to be a harmony, nor the reason of an organ,—as Aristotle says {2 De AnimaY of sense that it is like the reason of an organ:—for the intellect has not a common operation with the body.

That Aristotle, by saying that the intellect is unshackled or separate, does not mean to exclude its being a part or power of the soul which is the form of the whole body, is clear from what he says at the end of the First Book of De Anima, against those who said that different parts of the soul are in different parts of the body: If the whole soul contains the whole body it is meet that each of its parts should contain some fart of the body. But this seems impossible. For it is difficult to conceive what part the intellect contains and how.

It is also evident, since the intellect is not the act of any part of the body, that its receptiveness is not that of primary matter: forasmuch as its receptiveness and operation are altogether without a corporeal organ.

Nor again is the infinite power of the intellect excluded, since its power is not ascribed to a magnitude, but is founded on the intellectual substance, as stated.