Commentaria in Summam contra Gentiles, Liber II

It remains to show from Aristotle's own words that he was not of the opinion that the agent intellect is a separate substance, as most have wished to attribute to him, but rather that it is a power of the soul ¹. And first, this must be shown; second, an answer must be given to certain authorities of his on which those who have held the contrary view founded their position ².

1. It is argued, therefore, first, because in Book III On the Soul, text 18 ³, he says that the agent and possible intellect are differences of the soul and are in the soul, while he concludes, speaking of the agent and possible intellect: It is necessary that these differences be in the soul.

2. Second, because the argument he adduces there shows that this is what he intended. For he argues as follows. In every nature in which potency and act are found, there is something like matter, which is in potency to the things of that genus; and something like an agent, which reduces potency to act. The intellective soul is of this kind, since it is at one time actually understanding and at another time in potency. Therefore in the nature of the intellective soul there is something like matter, namely the possible intellect, which is in potency to all intelligibles; and something like an efficient cause, namely the agent intellect, which makes all things actual. — From this demonstration, therefore, it is clear that he intended both intellects to be in the nature of the soul, and not something separate in its esse from the body.

It must be noted that when the possible intellect is said to be in potency with respect to all intelligibles, and the agent intellect is said to make all things, the word all does not effect a distribution over all things simply, but over all material things, which are the proper and natural objects of our intellect, as is said in Book III of the Soul ⁴ For the sense is that the possible intellect is receptive of the species of all material quiddities; whereas the agent intellect is by nature apt to make all material quiddities actually intelligible, since in themselves they are only intelligible in potency.

3. Third, because in the same place he says that the agent intellect is like a habit which is light. Here it is clear that he does not call the habit the effect of the agent intellect, but the agent intellect itself, insofar as it makes man understand all things, and whenever he wills. But a habit is not signified as something subsisting in itself, but as belonging to something that has it. Therefore etc.

Saint Thomas also adds, for greater clarification, that here habit is not taken as it is in the second species of quality, as certain people said that the agent intellect is a habit of first principles; since that habit is received from sensible things, as is proved in II Posterior Analytics, last text, and thus it would have to be an effect of the agent intellect. But it is taken as divided against privation and potency: just as every form and act can be called a habit. This is clear because the agent intellect is said to be a habit as light.

It must be noted here that from the words of Saint Thomas it appears that the habit of the first principles, which are said to be natural to us and to inhere in us by nature, are not so called natural, or said to inhere in us by nature, as though they were formally congenital to us and implanted in us from birth itself; for if they were in us from generation in themselves and formally, they would not be acquired from sensible things, as Saint Thomas says here. But they are said to be natural to us because they are not caused by discourse and argumentation, but immediately by the agent intellect making phantasms actually intelligible; which intellect indeed is present in us from birth itself, and naturally, and with the phantasms of terms that are present to all, it produces those habits in the possible intellect. It does not, however, produce other habits naturally and of itself immediately with phantasms: but the possible intellect itself, by discoursing and arguing, causes those others in itself; although for their causation the power and light of the agent intellect also concur. Hence too on Boethius On the Trinity, last article, ⁵, Saint Thomas says that things of this kind known naturally to man are made manifest by the light of the agent intellect, which is natural to man.

It must also be noted that, when it is said that the agent intellect is a habit as light is, according to the teaching of St. Thomas in Qu. de Anima, art. 4. ad 4, Aristotle understands this comparison with respect to necessity, but not with respect to function. For just as color cannot be seen without light, so material things without the agent intellect are not actually intelligible, in the manner explained above at ⁶. But the function of the light of the agent intellect is to make the very phantasms, which are the object of the possible intellect, actually intelligible, by giving them the power whereby they can move the intellect. Bodily light, however, does not give color the power to move sight: since, as is said in II de Anima ⁷, color is visible in itself; rather, it makes the diaphanous actual, so that it can be moved by color. And in this sense the words of Aristotle are to be understood.

II. To these arguments, some, judging that Aristotle's mind was that the agent intellect is a separate substance, reply ⁸.

To the first, they say that by those words * Aristotle does not intend that in the soul there are agent and patient such that one and the same soul in number is agent and patient through different powers; but only that these differences are in the soul as they are in every other nature. Now it is clear that they are not in every nature in such a way that one nature in number has both of them as its subject has accidents; rather, they are as causes are in their effect. Therefore it must be understood only in this way that they themselves are in the soul*.

By this, too, the answer to the second objection is clear. For Aristotle's argument proves only that in the nature of the soul there must be these differences—agent and patient—just as in every other nature there are agent and patient; and it is evident that these need not belong to one and the same numerical substance.

To the third, it is said that the likeness between the agent intellect and a habit and light is not between the intellect in itself and a habit and light, but between their manner of acting, namely in operating when we will. Hence it does not follow that, if a habit is in us but is not a separate thing, then likewise the agent intellect is in us and yet is not a separate substance.

III. But that these replies are not in accord with Aristotle's mind is easy to see, if the force of his argument has been shown. Hence first that argument must be expounded; then the replies given will be set aside ⁹.

For the evidence of the argument, therefore, it must first be considered that, since "nature" is said in many ways, as is clear in Book V of the Metaphysics * ¹⁰, "nature" is taken here insofar as it signifies the quiddity and essence of a natural thing, namely one generable and corruptible, as is clear from the Commentator, On the Soul III, commentary 17. And the comparison of the natural thing to the soul is made according to the Commentator ¹¹ because the soul is one among natural beings, whether that be the quiddity of a genus or of a species. The name "genus" is likewise taken in a similar signification in this place, when it is said: In every nature there is something that is matter for each genus.

It must be considered, second, that when it is said that in every nature there is something which is in potency to all the things of that genus, this is not to be understood as though that thing were one in number; rather, it is one according to the unity of that nature. For the proper matter receptive of all the forms of a horse is not one in number, just as neither is there only one form of a horse in number. But if the nature is one according to species, then the proper recipient of the form must be one according to species, speaking proportionally: for instance, the flesh receptive of this or that form of a horse is the same according to species, and likewise the same bone and the same sinew according to species, and so with the rest. If, however, the nature is one according to genus, then the proper matter receptive of the forms of that genus must necessarily be one according to genus: for the forms of one and the same genus, say animal, require proper recipients of one genus, since matter and form must be proportioned to each other.

It must be considered, thirdly, that "act" is here taken not for operation but for the form that is a first act. Hence, when it is subsumed in the argument that the intellective soul is sometimes understanding in potency and sometimes understanding in act, "understanding in act" is not taken only in the second sense of act, which is to operate; but also in the first sense of act, which is to possess the form by which the intellect is in act.

It must be considered, fourth, that although the intellective soul is a certain act according to its substance, yet as intellective—that is, as ordered to intellection—it is sometimes in complete first act, namely when it has within itself the intelligible species; but sometimes it is not in complete first act, but is in potency with respect to something, as when it does not have the intelligible species. For then it is said to be in potency because it lacks all that is required for it to be able to pass into operation. Therefore the Philosopher here speaks of the intellective soul insofar as it is intellective, by comparison with natural things, which are sometimes in act and sometimes in potency.

Finally, it must be considered that in this argument the Philosopher presupposes two things determined by him above. One is that the soul has within itself, as properties, those powers required for understanding. For he said this when enumerating, in Book II of De Anima ¹², the intellective power among the powers of the soul; and in Book III, when beginning to treat of the intellect, he says ¹³: "But concerning that part of the soul by which it understands and knows," where he calls the intellect a part of the soul. — The other is what he had said immediately before this argument ¹⁴, namely, that material things are not intelligible except in potency: from which it follows that they are not sufficient of themselves for the actualization of the possible intellect.

From all these points it follows that the comparison of other generable and corruptible natures with the soul, as regards the active and passive principle, is not as to the mode of having them, but as to the necessity of having them, each thing nevertheless in its own way. And the comparison is such as this: that just as in a material nature proceeding from potency to act, there must be a [passive] principle of all the forms of that nature, and an active principle of them, as contained under that nature (for the principles of the species are in that species reductively); so in the intellective soul, insofar as it is sometimes in act, as intellective, and sometimes indeed in potency, since the intelligible object does not suffice to act upon the intellect, there must be those differences of active and passive in its own way, namely, by way of properties existing in the one substance of the soul itself; for every principle principally required for intellection must be in the intellective soul as its passion and property. For Aristotle suggested this understanding of the comparison when, after the comparison, he added that the active element in the soul is intellect in making all things as a certain habit. For a habit is in the subject of that of which it is the habit: as Saint Thomas assumes in the third argument ¹⁵.

IV. These points having been set out, it is clear that Aristotle's argument concludes the proposed conclusion, as Saint Thomas formulates it ¹⁶, arguing as follows. In every nature in which potency and act are found, there is something like matter receptive of the forms of that genus, and something like an agent, both belonging to that nature as principles in their own way. But in the intellective soul there are act and potency, since it is sometimes actually understanding in the first way, and sometimes in potency. Therefore, in its nature there is something like matter, namely the possible intellect, and something like an active principle, namely the agent intellect, belonging to its nature, insofar as it is intellective, in their own way. But (supply) the mode of the soul's having the principles by which it is made actually intellective from being potentially intellective is such that they are potencies and properties of it, since understanding is a potency of the soul. Therefore, the agent and possible intellects are in the soul as its potencies; they are not separate substances. — Behold, therefore, how Aristotle's argument shows, as Saint Thomas said, that the agent intellect is not a separate substance. And thus there is no reply to the first and second arguments of Saint Thomas.

That the response to the third argument is also no response is clear from the words of the reply. For, granting that that assimilation is according to the mode of acting of the intellect and of the habit, since we act by both when we will, the argument runs thus. That which we use in acting when we will is not a separate substance, but is in us. But, by your own account, we use the agent intellect in acting when we will, as we use a habit. Therefore it is not a separate substance, but is in us. — The major is proved. Because the operation of forms most separate from matter and belonging to a higher order of things is not within our power, so that we could exercise that operation at our own discretion. For that is not voluntary whose principle is outside, but whose principle is within us ¹⁷. Therefore, etc.

V. As to the second point ¹⁸, Saint Thomas expounds certain authorities of Aristotle from which those who hold the contrary opinion might argue. There are five of them.

The first is in III de Anima, text 19, where Aristotle says that the agent intellect is separate and unmixed. From which it is argued: The agent intellect is separate and unmixed. Therefore it is not in the soul, but is a separate substance.

The second argument is in the same place. For he says that the agent intellect is a substance actually being. But nothing is at once in act and in potency with respect to the same thing. Therefore, since in the soul there is the possible intellect, by which it is in potency, there cannot be in it an agent intellect.

Third, there is the same passage ¹⁹, where he says that knowledge of a thing is one with it in act. The Commentator, expounding this, says that in the agent intellect the one understanding and the understood are the same, but not in the possible intellect. Therefore the agent intellect is separate: because only in things separate from matter are the one understanding and the understood the same.

The fourth is in the same place, text 20, where he says that the agent intellect does not at one time understand and at another time not understand. But nothing of this sort is in us. Therefore, and so on.

The fifth is in the same text, where he says: But only that which truly is is separate, and only this is immortal and everlasting. Therefore it is not in us.

VI. To the first of these authorities Saint Thomas responds by explaining Aristotle's mind concerning the conditions attributed to the agent intellect in comparison with the possible intellect, namely that Aristotle did not say the agent intellect is separate from the body, but from the bodily organ; which he had also said above concerning the possible intellect. He proves this by the following argument: since the agent is nobler than the patient, and the active than matter, if the possible intellect is separate from the organ, much more will the agent intellect be separate from the organ.

2. To the second he responds that this is not repugnant to the fact that the substance of the soul is in potency, as was shown in the preceding chapter. For there it was shown that it is not unfitting for the soul to be in act and in potency with respect to different things.

3. To the third he says two things. The first is that the Commentator's exposition is against Aristotle's mind. For it is not true that the possible intellect in act is not the intelligible itself, since the Philosopher asserted this of it above, texts 14 and 15; indeed he said this even of sense and the sensible in act above, text 3 ²⁰.

He says second, that Aristotle does not speak these words of the agent intellect, but of the intellect in act. For after he had determined concerning the possible and the agent intellect, it was necessary to determine concerning the intellect in act. Of this he first states its difference from the possible intellect, in that the intellect in act, or science in act, is identical with the thing known, but the possible intellect is not. He adds afterward, as another difference, the order of the possible intellect to it: because the latter, insofar as it is in potency, is prior in time to the intellect in act in one and the same thing; but not simply, since it is reduced to act by the agent intellect and also by the intellect in act.

It must be noted here that, when it is said that science in act simply precedes intellect in potency, even in time, although within one individual the reverse is the case, this is not to be understood of potency taken absolutely. This is evident because, if we take by intellect in act the agent intellect itself, it is clear that intellect in potency does not precede it in duration in the same subject, since they exist together in the soul. — But if we take the habit of the first principles, or the intellect actualized by that habit by which one discovers science by oneself: thus too it is manifest that intellect in act does not precede in time the potency of the intellect with respect to other intelligibles. Rather, it follows upon and is posterior to that potency, since from its generation the intellect is in potency, but it is not actualized by such a habit from its generation. — If finally by intellect in act we take the intellect of the teacher, it is likewise not necessary that it precede in time the potency of the learner. For if the learner is older in substance than the teacher, he is first understanding and knowing in potency before the teacher is knowing in act. — It remains, therefore, that it be understood of the potency which is being moved toward act. For it is now most true that the intellect is moved toward science in time before it has science: because, since science is acquired through a certain discursive process, the intellect must first acquire cognition of the principles before the scientific habit of conclusions is caused in it, whether it is acquired through discovery or through teaching. Similarly, intellect in act must precede in time intellect in potency, namely insofar as it is moved toward an act opposed to that potency: for both the intellect possessing the habit of the first principles and the teacher's intellect actualized by science must exist before the possible intellect of the learner is moved to the act of science.

This exposition is clear from the argument that Saint Thomas adduces both here and in III de Anima ²¹: namely, that a potency is not reduced to act except by something existing in act. Now it is evident that from the fact that a potency is not reduced to act except by an ens in act, it does not follow that the act precedes the potency, taken absolutely, in time, but rather the very actualization of the potency: for the agent must exist before it moves the potency to complete act, where something is reduced to act successively, as the intellect is reduced to the act of true science. The sense, therefore, will be that in one and the same subject the potency of the intellect which is moved to the perfect act of science precedes that science simply; yet the knower in act also precedes the potency in time—that is, the motion of the potency toward act, or the potency as being moved to act.

That this interpretation of Aristotle's words concerning the intellect in act accords with his mind, and not that the object of the knowledge of the agent intellect is the agent intellect itself, is apparent because he does not say that the agent intellect, or that its knowledge, is identical with the thing—which would certainly have had to be said if the agent intellect were meant—but speaks absolutely, as beginning a new proposition: "But knowledge in act is identical with the thing; while knowledge in potency is prior in time in one respect."

4. To the fourth he replies that Aristotle does not say those words about the agent intellect, but about the intellect in act ²². For the intellect in act also differs from the possible intellect, because the possible intellect sometimes understands and sometimes does not understand; but this cannot be said of the intellect in act, which is the intelligibles themselves in act.

Note that Saint Thomas, in the Prima, q. 79, a. 4, ad 2, says that if the aforesaid words are understood of the agent intellect, they are to be expounded thus: namely, that it is not on the part of the agent intellect that we sometimes understand and sometimes do not, but on the part of the possible intellect.

Some Thomists reject this interpretation of St. Thomas placed here ²³, saying that it should have been excluded from anyone's mind as doubtful that the intellect in second act sometimes understands and sometimes does not understand: for it is certain of every operating act that it does not sometimes operate and sometimes not operate. But they do not see that Aristotle did not say this as though it were doubtful to some: but because, as is said in the Spiritualibus, art. 10, ad 3, since his purpose was to explain the differences between the intellect in act and the possible intellect, after he had explained two — namely, that the intellect in potency is not the intelligible in potency, but the intellect in act is the intelligible itself in act; and that the intellect in potency precedes the intellect in act in time in the same subject, while the intellect in act simply precedes the intellect in potency — he adds a third difference, namely that the possible intellect indeed sometimes understands and sometimes does not understand; but it is not so with the intellect in act, as is manifest, since the intellect in act consists in the very act of understanding.

5. To the fifth he says, following the context of the preceding words, that those words are said neither of the agent intellect nor of the possible intellect, but of the whole intellective part. Not of the agent: because he had already said the same of the possible, and thus the agent would not alone be separate. Nor yet of the possible: because he had already said the same of the agent, and thus it could not belong to the possible intellect alone. Hence it remains that they are to be understood of that which comprehends both, namely of the intellect in act, of which he was speaking. For this part alone of the soul, namely the intellective part, is said to be separate because it does not use a bodily organ. And therefore he adds concerning the same that this alone is immortal and everlasting, as not depending on the body.

It must be noted here that the intellect in act is called immortal and perpetual, not by reason of its operation, through which it is made to be in act, as if any one of its operations were perpetual; but by reason of the agent intellect and the possible intellect, which it comprehends, as required for it to be an intellect in act.