Commentaria in Summam contra Gentiles, Liber III

Having excluded Avempace's position, St. Thomas wishes to exclude Alexander's position as well ¹. Whence first he explains his position, as it is recounted by Averroes in III De Anima ², and compares it to the opinion of Avempace; secondly, he refutes it ³; thirdly, he replies to his argument ⁴.

I. First, then, Alexander posited that our possible intellect can never arrive at knowing separate substances: because it is generable and corruptible, as being a preparation of human nature consequent upon the mixture of elements, as was held in the Second Book.

He posited secondly that, this notwithstanding, we can, according to the state of the present life, understand separate substances. Because when each thing has reached the completion of its generation and the ultimate perfection of its substance, its proper operation—whether action or passion—is completed; when the generation of the habitual intellect, which is nothing other than intelligible species made by the agent intellect existing in the possible intellect, has been completed, namely when it acquires no more new species, its twofold operation will be completed; for it will make all potentially understood things to be in act, which is the completion of that operation of its which is to make potentially understood things to be understood in act; it will also understand all intelligible things, separate and non-separate, in which is completed its second operation, which is to understand things understood in act. — How one operation is an action and another a passion was shown above in this third book, chapter XXII.

He posited thirdly that, since the possible intellect cannot understand such substances, we will understand them through the intellect in habit, inasmuch as the agent intellect, which according to him is a separate substance, will become the form of the intellect in habit in ⁵ ourselves, so that through it we will understand just as we now do through the possible intellect: since it belongs to it to make all potentially intelligible things to be understood in act, and to understand separate substances.

2. From these points it follows first, that through cognition which is from phantasms we arrive at cognition of separate substance, not as though understood phantasms were the medium for knowing them, as happens in the speculative sciences, according to the opinion of Avempace: but inasmuch as intelligible species are certain dispositions in us toward such a form as is the agent intellect.

It follows secondly, that ultimate human perfection is not in the speculative sciences, as Avempace posited: but through them man is disposed toward attaining ultimate perfection, namely to the end that the agent intellect may become a form for us. And Alexander calls the intellect thus formed the acquired intellect, of which some say Aristotle says that it is from without.

It follows thirdly, that by the fact that the agent intellect is conjoined with us as a form, we understand it and other separate substances: but understanding the agent intellect is not the cause of its being conjoined with us, as Avempace maintained.

3. Because St. Thomas, in the second claim of Alexander's position, says that man through the intellect in habit, or through the intellectual habit, makes intelligibles in act, while in the third claim he says that this is done through the agent intellect: it must be considered that this is attributed to both of them, but in different ways. For we can speak in a twofold way concerning the intelligible in act: namely, with respect to first act, and with respect to second act. To be intelligible in first act is to be abstracted from matter, and to be united to the intellect after the manner of a form by which it understands. But to be intelligible in second act is to be actually presented as an object to the act of understanding and to be its term.

With respect to this, therefore, we can posit a distinction between the agent intellect and the intellectual habit, which is called by another name the intelligible species, in a threefold way. In one way, because the agent intellect makes intelligibles in first act, inasmuch as it causes in the possible intellect intellectual species abstracted from phantasms. But the intellectual species makes intelligibles in second act, inasmuch as the intellect, having been made in act through the species, forms a concept in which the thing is actually presented to it as an object as the intrinsic term of the act of understanding. - In the second way, by comparing both to the first act. Because the agent intellect makes intelligibles in first act efficiently: but the intelligible species formally, because the species itself is that by which the thing is said to be actually intelligible in the intellect. - In the third way, by comparing both to the second act. Because the agent intellect makes intelligibles in second act mediately: but the species immediately, as the form through which the possible intellect produces the concept and the word. Therefore St. Thomas says that the intellect in habit has this action—which is to make potentially intelligible things to be intelligible in act—on the part of the agent intellect.

II. Against this opinion St. Thomas argues first as follows ⁶. The intellect in habit, just like the possible intellect, is posited by Alexander to be generable and corruptible. Therefore it is impossible for the agent intellect to become its form. - The consequence is proved. Because, according to him, the agent intellect is posited as a certain eternal separate substance. But what is eternal cannot become the form of a generable and corruptible thing, according to him, who on this account posits the possible intellect to be generable and corruptible because it is united to us as a form.

Note that this proposition of Alexander, An eternal thing cannot be the form of a generable and corruptible thing, is not universally true, for the intellective soul can be eternal, namely produced from eternity, and yet is the form of a generable and corruptible thing, namely the human body: but it has truth concerning a form dependent upon matter according to esse. For it follows: It depends upon matter according to esse: Therefore it cannot be without matter: Therefore, matter being corrupted, it too is necessarily corrupted: Therefore it is not eternal. But even if something is eternal (I call eternal that which does not have a beginning of its duration), it is not repugnant to it that it be the form of a corruptible thing elevated above it, and not depending on it according to esse.

III. Secondly. The form of the intellect, inasmuch as it is intellect, is an intelligible: since the intellect does not receive anything, properly speaking, except intelligibly. Therefore, if the agent intellect cannot be an intelligible through the intellect in habit, it is impossible for it to be its form.

It must be noted that this argument concludes that two claims of Alexander cannot stand together: namely, that the agent intellect is the form of the intellect in habit; and that the intellect in habit does not understand the agent intellect, but is only a disposition toward the agent intellect being united to us as a form so that we may understand through it, as Alexander held.

Concerning what is said, that the intellect receives nothing, properly speaking, except intelligibly, it must be observed that he added properly speaking because per accidens, that is, by reason of the sensitive powers, it can be said to receive something non-intelligibly: for instance, when, an organ of the imagination having been injured, it is hindered from its operation; for then it is said to receive per accidens, because that which it needs for its operation is materially altered, and materially received.

IV. Thirdly. If man at some time understands separate substances through the agent intellect, he will understand by it either as by an intellective power from which proceeds the operation which is both the intellect's understanding and our understanding; or as by an intelligible species by which the intellective power is perfected; or as by a medium through whose cognition we arrive at the cognition of another. Not the third: because neither the possible intellect nor the intellect in habit, according to Alexander, understands the agent intellect. - Nor also the second: because understanding through an intelligible species is attributed to the intellective power of which that intelligible species is the form; but Alexander does not concede that the possible intellect, or the intellect in habit, understands separate substances. - Finally, not the first: because the understanding of the agent intellect would be the understanding of man; but this cannot be, according to Alexander's position, because then the agent intellect would not be a separate substance, as he himself held. The sequel is proved. Because it cannot be that the understanding of man and of the agent intellect are the same unless from the substance of the agent intellect and the substance of man there becomes one according to esse: since it is impossible for there to be two diverse substances according to esse, and that the operation of the one be the operation of the other. But from them there will not become one according to accidental esse: because then the agent intellect would not be a substance. Therefore according to substantial esse. Therefore it will either be the human soul; or a part of it, namely potential; and consequently not a separate substance.

2. Concerning that proposition, It is impossible for there to be two diverse substances according to esse, and that the operation of the one be the operation of the other, it must be noted, from the doctrine of St. Thomas, In III Sent., d. XVIII, a. 1, ad 5, that an action can be called one in a twofold way: namely, simpliciter; and by aggregation. Similarly, the operation of the one can be called the operation of the other in a twofold way: namely, simpliciter; and by adjunction. The operation of the one is said to be the operation of the other simpliciter when the numerically same operation that proceeds from the one also proceeds from the other: and thus this is impossible. But according to adjunction, when the operation of the one is adjoined to the operation of the other for the production of one effect: which happens when one agent cannot accomplish the effect per se, but many at once; just as, when many drag a ship at once, there are many actions simpliciter, as the action proceeds from the agent, but there is one action by aggregation; and the action of the one can be called the action of the other, inasmuch as the one is helped by the action of the other to complete the effect. St. Thomas speaks, therefore, in the first sense, not in the second.

V. Fourthly. By the same reason that the agent intellect will become at some time the form of this man, by the same reason it will of another as well. Therefore then two men will understand through the agent intellect as through their form. Therefore there will be the same understanding of two understanding subjects: since man would so understand through the agent intellect that its understanding would be the understanding of the one understanding through it. But this is impossible. Therefore etc.

VI. To the foundation of Alexander's position, namely that the completion of the operation of the intellect in habit is to understand separate substances, St. Thomas replies by denying it ⁷. And first, he replies to his argument: saying that, when the generation of any genus is perfected, its operation is indeed perfected, but nevertheless according to the mode of its own genus, not however according to the mode of a higher genus. And thus, the intellect in habit having been completed, its understanding is completed according to its own mode: but not according to the mode of separate substances, so as, namely, to understand separate substances.

2. Secondly, he proves that that foundation is false, in a twofold way. First because, if to understand separate substances were the completion of the operation of the intellect in habit, it would at some time understand separate substances. And consequently, through the speculative sciences, which are contained under the intellect in habit, separate substances would be understood. Which Alexander does not posit.

Secondly, because understanding separate substances would follow upon those who study toward the generation of the intellect in habit, either always or for the most part. For since, of those things that begin to be generated, generation is completed for the most part; if to the completion of generation there follows the completion of action, the completed operation must arrive for the majority of the things that are generated. But this is evident to be false: indeed no one has professed that he has arrived at this perfection. Therefore etc.

3. Concerning the first of these arguments it is doubted: since St. Thomas says that Alexander does not posit that the intellect in habit at some time understands separate substances. For this seems to contradict that which he recounted above ⁸ in the second claim of Alexander. For there he said Alexander wished that, the intellect in habit having been completed, its second operation will be completed, by the fact that it will understand all intelligible things, separate and non-separate.

It is answered that Alexander posited, as is clear from the things said above ⁹, that the intellect in habit does not understand separate substances as that from which the operation itself proceeds: and thus St. Thomas intends in this first argument. Yet he posited that through it man understands inasmuch as it is a disposition toward the agent intellect being united to us as a form through which we may understand. Whence the intellect in habit is said, in Alexander, to understand separate substances, not formally indeed, but dispositively. And thus St. Thomas understood above.