Commentaria in Summam contra Gentiles, Liber II

After St. Thomas has determined concerning intellectual substance with respect to its nature, he begins to determine concerning it with respect to its union with the body¹. Concerning this, however, he does two things: first, he shows that some intellectual substance is united to a body; second, that besides this one there are others not united to bodies, chapter XCI.

As to the first, he does two things: first, he shows that the rational soul is united to the body; second, he inquires to what sort of body it is united, chapter XC.

Concerning the first, he does three things: first, he treats of the union of the intellectual soul with the body in itself; second, of its duration before and after that union, chapter LXXIX; third, of its production as the cause bringing about the said union, chapter LXXXVI.

On the first point he does two things: first, he determines concerning the substance of the intellective soul itself as united; second, concerning its powers, which are the possible intellect and the agent intellect, chapter LXXIII.

As to the first, he does two things: first, he shows what is manifest in this difficulty; second, what is doubtful, concerning the middle of the present chapter².

I. As to the first point, three conclusions are proposed³. The first of which is: An intellectual substance cannot be united to a body by way of mixture.

It is proved first. An intellectual substance does not share in matter with corporeal things, since it is immaterial. Therefore they do not alter one another. Therefore they are not mixed. — The first consequence is proved. Because only things that share in matter, which can be active and passive with respect to one another, can be altered by one another. — The second is also proved. Because things that are mixed must be altered by one another.

Second. Those things that are mixed, once the mixture has been made, do not remain in act but only in potency. Therefore etc. — The antecedent is proved. First because, if they remained, there would not be a mixture but merely a confusion. Second also by a sign: because a body mixed from the elements is none of them. — The consequence is also proved. Because intellectual substances are incorruptible.

II. For the clarification of this proposition, Those things that are mixed, once the mixture has been made, do not remain in act but only in potency, as is evident from the elements in a mixed body, it must be known that this proposition is taken from the Philosopher in the book On Generation, ⁴ where he holds that in true mixture each of the mixibles must be corrupted, and from these things thus corrupted some third thing must be generated. On account of which he says in the Second book ⁵ that if a drop of wine is added to a thousand amphorae of water, no true mixture results but rather a corruption: namely because the drop of wine loses its species and is transformed into water; but in a mixture one of the mixibles must not be converted into the other, but both must be corrupted and converted into a certain common mean.

2. But how the miscibles are said to remain in the mixture in potency is explained by the Thomists in two ways. For some understand it thus: that from the qualities of the elements, when remitted, there results a middle quality really composed of parts of different rationes, having something formally of heat and something of coldness, and so with the others; so that sometimes one of its parts is intensified and another remitted, and accordingly the mixture draws nearer to this element or to that one.

This opinion, however, has its foundation in the words of St. Thomas. First, because in the First Part, q. 76, a. 4, ad 4, he says that in a mixture there remain the proper qualities of the elements, but remitted, and in these lies the power of the elementary forms. — Second, because De Malo, q. 5, a. 5, ad 6, he says that contrary qualities in a mixed body are regulated and preserved so that they do not corrupt one another, by the substantial form. — Third, because in the treatise entitled How the elements remain in a mixture ⁶, he says that, once the excellences of the qualities of the elements have been remitted, there is constituted from them a mean quality, which is the proper quality of the mixed body, differing in different cases according to the different proportion of the mixture. — Fourth, because in IV Sent., d. 44, q. 1, a. 1, q^a. 1, ad 4, he says that the form of the mixture is a quality resulting from the simple qualities as they come to a mean. — This can also be gathered from him at the end of the first book On Generation ⁷, where, expounding those words, Mixture is the union of altered miscibles, he says that this alteration is to be understood only in their powers or qualities. But if alteration is taken improperly, mixture is the union of altered miscibles, that is, of corrupted ones, according to their forms. For this can be understood thus: that the very substances which are mixed are not properly united, as if they remained in their own substance while altered; rather they are corrupted and cease to be: but it is their qualities that are united and remain altered, that is, remitted from their excellences. — Thus it is established that the quality of the mixture is something composite, made up of the qualities of the things mixed, remitted and reduced to a mean.

This can also be had from Aristotle, III Topic., chapter V ⁸, where he says that is whiter which is less mixed with black: where he seems to intend that the extremes are contained in act in the mean.

3. Others, however, say that from the corrupted qualities of the elements a middle quality is generated, simple indeed in act, inasmuch as in it there is no actual diversity of hotness and coldness or of the other qualities, but multiple virtually, insofar as the qualities of the elements are contained in it virtually.

That this is the mind of St. Thomas is proven from his own words in III Sent., d. xiv, a. 2, q^a. III, ad 1, where he says that in less white there is nothing of blackness, but whiteness of lesser intensity: from which he seems to wish that in the mean the extremes are not in act.

4. Either of these opinions could also be sustained in the doctrine of Saint Thomas. For if one holds the first opinion (which Capreolus also holds, II Sent., d. xv, in his reply to the last objection against the second conclusion ⁹), one can answer the objection raised against it from the words of Saint Thomas in two ways. First, that the case of the qualities of the elements is not the same as that of color: for those are primary qualities; color, however, is a secondary quality, resulting variously from the diverse mixture of primary qualities. — Second, that Saint Thomas is speaking of the less white which with the more white is of the same species: but not of the less white which is of another species than white, as red or green is, which is properly a mean between white and black, just as the quality of complexion, or of mixture, is a mean between the qualities of the elements; for in such a less white there is also something of blackness.

Holding, however, to the second opinion, one may say in response to the authorities adduced above that it suffices for the mind of St. Thomas that the qualities of the elements be contained virtually in the complexional quality.

But with respect to Aristotle it may be said that by black he does not understand a quality, but the privation of whiteness. For the sense of his words is that something is called whiter which has less of the privation of whiteness—that is, which has a more perfect whiteness.

III. The second conclusion is ¹⁰: An intellectual substance cannot be united to a body by way of contact properly so called. This is evident, because such contact belongs only to bodies.

Corollary: An intellectual substance and a body cannot be made one by continuation, or composition, or binding together: since these plainly cannot occur without contact.

IV. Third conclusion: It is possible for an intellectual substance to be united to a body by contact of power. For such contact consists in acting. But intellectual substances act upon bodies and move them, since they are immaterial and exist more in act.

For the manifestation of this, however, the text posits a threefold difference between contact by virtue and bodily contact. For in contact by virtue, an indivisible thing can touch a divisible one; such contact occurs not only at the extremities but also with respect to the whole; it is also directed to the innermost parts, and makes the substance of the one touching be within that which is touched; none of which is found in bodily contact.

It must be noted, concerning the second and third differences, that the passive potency by which a corporeal thing is said to be acted upon or moved by a spiritual substance is the potency of the composite substance, not of the quantitative extremity. For a surface in itself has no potency for being acted upon, even though the substance is in potency to colors by means of the surface: just as an accident does not have esse of itself, so being acted upon does not properly belong to it. And because the potency of a composite thing is intrinsic to it, therefore, since the substance is there where it acts, it is necessary that the spiritual substance which touches the body be intrinsic to it and move through it, touching it, namely, by its own power—since there is nothing in that body that would impede the intellectual substance from acting intrinsically, just as the bulk of a body prevents another body from touching its intrinsic parts. — How an intellectual substance is in place through contact of power will be said in Book Three ¹¹.

V. As to the second point ¹², Saint Thomas shows what in the very difficulty is doubtful.

First, he shows the reason for doubting. For since from mere contact of power there does not come about one thing simply, since to be one in acting and being acted upon is not to be one simply, it is not sufficient for an intellectual substance to be said to be united simply to a body that it be united to it according to power; rather, from the intellectual substance itself and the body there must come to be one thing, either as an indivisible, or as a continuum, or as one by reason. Now it is certain that from an intellectual substance and a body there cannot come to be one as an indivisible, since they are two; nor by continuity, since the intellectual substance plainly has no quantity. There remains, therefore, only this to be investigated: Whether from them there can come to be one thing simply, one by reason and essence. And because from two permanent things there comes to be one by reason only as from matter and form, the doubt is: Whether an intellectual substance can be the substantial form of some body.

Second, he enters into the inquiry of the difficulty raised. Concerning which he does four things principally: first, indeed, he sets forth the arguments on the false side; second, he recounts the opinions of others, in the following chapter; third, he determines the truth, in chapter LXVIII; fourth, he resolves the arguments brought forward in opposition, in chapter LXIX.

VI. He therefore first sets out five arguments showing that an intellectual substance cannot be united to a body as its substantial form.

The first of these is: because from two substances actually existing, nothing one can be made.

Second: because intellectual substance and body are different genera; but form and matter are contained within the same genus.

Third: because it would follow that an intellectual substance is not immaterial, since its esse would be in matter.

Fourth: because the intellect is shown by the philosophers to be separate from the body.

Fifth: because it would follow that the operation of the intellectual substance is common to the body, just as its esse is.