Commentaria in Summam contra Gentiles, Liber II

After St. Thomas has shown that the possible intellect is not a separate substance nor one in all, he now wishes to demonstrate the same concerning the agent intellect ¹. Concerning this, however, he does three things: first, he shows that it is not a separate substance, but something of the soul; second, he declares how it is not impossible for it to be joined with the possible intellect in one substance of the soul, in the following chapter; third, he shows that this is so according to the mind of Aristotle, in chapter LXXVIII.

I. As to the first, it must be known, as is said in the Questions on the Soul, article 5, that the agent intellect being one and separate seems to have more reason on its side than if this were posited of the possible intellect: because a separate agent is found among those things which reduce something into act; but that by which something is in potency seems to be altogether intrinsic. And therefore more thinkers posited the agent intellect to be a separate substance than the possible intellect. For this reason Saint Thomas holds that, besides Averroes, Alexander and Avicenna also posited the agent intellect to be one for all.

Against this opinion it is argued, by proving that the agent intellect is something of our soul.

And it is argued first ² thus. Agent and patient must be proportionate to one another. Therefore to each passive there corresponds its own proper active principle. Therefore, if the possible intellect is something of the soul, multiplied according to the multitude of individuals, as has been shown, then the agent intellect will be of this kind. — The last consequence is proved. Because the possible intellect stands to the agent as its proper passive or receptive counterpart: since the agent intellect is related to it as art to matter, as is said in Book III On the Soul.

Note that the antecedent must be understood of the proximate agent, not of the remote agent. For the remote agent need not be proportioned by way of adequation to every recipient: since one remote agent can act upon many recipients. But the proximate agent must indeed be proportioned. For we see in natural things that to every effect, especially in perfect things, there corresponds a proper agent: for a rose is not produced except from a rose, and a horse is produced only from a horse; and thus to the proper receptive matter of the form of a rose, and to the proper receptive matter of the form of a horse, there correspond proper agents. Now the agent intellect is posited as the proximate agent with respect to the possible intellect. Therefore they must be proportioned to one another.

Note also that the agent intellect is said by Aristotle to be compared to the possible intellect as art to matter: for just as art, operating principally, reduces matter from potency into act of the form of art, but not into the natural form of the one operating by art—for the house-builder produces by his art the form of a house in matter, but not his own form whereby he is a man—so the agent intellect introduces into the possible intellect the intelligible species of natural things, and reduces it from potency into act with respect to those things; but it does not introduce into it its own form according to which it is the agent intellect.

II. But this argument seems not to conclude. For it could be said that, although the agent intellect corresponds to the possible intellect as its proper active principle, and is of one species, just as every possible intellect is of one species, it does not follow that one agent intellect in number must correspond to one possible intellect in number; since we see that one agent in number can act upon many passive things, as one fire in number can burn many pieces of wood, and by one art of building many materials can be transformed into the form of a house.

Granted also that there would have to be as many agent intellects in number as there are possible intellects, it still does not follow that, if the possible intellect is something of the human soul, the agent intellect is also something of the soul. For the agent need not be rooted in the same essence in number as the patient, since we see that in natural things the agent is entirely separate from the patient according to its substance, as fire is from wood.

III. The reply is given, and it is said first that not all the arguments adduced here by Saint Thomas are to be taken as demonstrations, but some are probable and persuasive. Hence it is not necessary in every case to strive to show that they conclude with necessity. I shall endeavor, however, as far as possible, to show that they are effective and of no small weight.

It is said second, that the proposition assumed as the foundation of the argument, namely, To every passive there corresponds a proper active, must be understood of the natural passive, and of identity of genus and order. For it is necessary that to what is naturally moved by something there correspond, as its proper and natural agent, some agent that is of the same genus with it, especially in perfect things, as is held below ³. Therefore it is said in VII Metaphysics ⁴ that material things cannot be produced by separate forms as by their proper actives, since they are of another order than they and of another genus. If, therefore, the agent intellect is compared to the possible intellect as its natural and proper agent, it is necessary that they be of the same genus and order. And therefore, if the intellect is an accident of the soul, or the form of the body (if it is not distinguished from the soul itself; for this has nothing to do with the matter at hand), and consequently is multiplied with the multiplication of men: it is necessary that the agent intellect also be an accident of the soul or the form of the body, and be multiplied with the multiplication of men. And thus it will not be one separate substance.

2. Hence, as to the objects, it is clear that they are not contrary to the mind of reason. For St. Thomas does not wish to conclude by this argument, first, that to each possible intellect there corresponds one in number agent intellect, as the objection supposes; nor that in the same numerical essence of the soul there must of necessity be a possible intellect and an agent intellect by which the former is moved; but only this: that there is no separate substance serving as a single agent intellect for all men. And this is most excellently concluded according to the declaration already made. This being so, given the mode of acting of the agent intellect and its necessity, it is consequently more fitting to say that the possible intellect of one man is moved by the agent intellect existing in that same man than that it is moved by an agent intellect existing in another man, as will be shown below by other arguments.

3. But if one presses against the explanation of the reason, because Saint Thomas says, according to the mind of Aristotle, that the agent intellect is compared to the possible intellect as art is compared to matter; yet art need not be of the same genus and order as the matter of art, since art has immaterial esse, but matter does not; and thus the explanation of the foundation of the reason seems not to be in accordance with the intention of Saint Thomas: — it is said that this comparison is true in a certain respect, but in another respect it does not hold true: just as happens in every other comparison. For the agent intellect is related to the possible intellect as art is related to matter, insofar as it does not produce its own species in the possible intellect, but only the forms of material things: for it does not cause another agent intellect in the possible intellect, but intelligible species, which are the forms of material things. So too the craftsman does not cause his own form and his own species, by which he exists in the nature of things, in matter, but causes only the forms of the things with which his art is concerned. Hence what Saint Thomas says, that the possible intellect is the proper passive or receptive principle of the agent intellect, must not be understood as though the agent intellect were received in it according to its proper species: but because it is that in which all forms produced by the agent intellect are received. — Now there is a dissimilarity between the agent intellect and art in their relation to what is passive, because the agent intellect is compared to the possible intellect as to its proper and natural passive principle, receptive of forms according to the same mode of being that befits the agent intellect, namely according to intelligible and immaterial esse: therefore both intellects must agree in their mode of being, so that, just as the possible intellect has esse in the manner of something inherent or of the form of another, so too the agent intellect may have esse. But art is compared to matter as to a receiver of form according to a different mode of being: for matter receives the form of art materially, whereas in the intellect it has immaterial esse. Therefore there need not be the same mode of being in art and in its receiver. Hence also art is not a natural active principle, but rather voluntary: insofar as it acts only when joined to the will. The agent intellect, however, is a natural active principle with respect to the possible intellect, although in a certain respect, as was shown above ⁵, it has the manner of an art.

It is further said that, although art has a different mode of being than matter, it is nevertheless not said to be of another genus and another order. For art is of the same rational character as the material form, and both modes of being are not repugnant to its rational character. For the material and the immaterial are then of different orders when to the rational character of one it is repugnant to be in matter, while to that of the other it is fitting that it be in matter: as a separate intelligence and a horse are of different orders and genera. But to the rational character of a form produced by art, insofar as it is such, neither being material nor being immaterial is repugnant. Hence, just as matter is of the same order and genus as the form introduced into it by art, so also with art itself.

IV. Second, ⁶ it is argued to the conclusion. The agent intellect makes intelligible species such as it itself is. And it makes such species as befit the possible intellect for understanding. Therefore it is proportioned to the possible intellect. Therefore, since the possible intellect is a part of the soul, it will not be a separate substance. — The first part of the antecedent is proved: because every agent acts in a manner like to itself. — The second part, however, is proved: because it does not make intelligible species in act so that it itself may understand through them, especially as a separate substance would, since it is not in potency (namely passive potency); but rather so that the possible intellect may understand through them.

V. Concerning this argument there is a twofold doubt. First, concerning the first part of the antecedent, it is asked how that likeness of quality between the agent intellect and the intelligible species is to be understood. For either it is understood that the species makes something of the same ratio as the intellect itself, or according to the same mode of being. If according to the same ratio, this is manifestly false: for the intelligible species of a stone, produced by the agent intellect, is not of the same species as the agent intellect, but as the stone existing in matter. — If according to the same mode of being, then the proof assumed for this will not be to the point. For not every agent acts upon what is like itself with respect to the same mode of being, although it does in some way make something like itself according to the same ratio: for it was shown above ⁷ how a form has one mode of being in matter and another in the mind of the craftsman.

Second, doubt is raised concerning the first consequence. For either the agent intellect is understood to be proportionate to the possible intellect according to the same ratio, and thus the consequent does not follow unless the antecedent is understood in the same sense, namely that the intelligible species is of the same ratio as the possible intellect and the agent intellect. But it is manifestly evident that this is false. And so there will be no argument at all. — Or it is understood to be proportionate according to the same mode of esse. And then the antecedent must likewise be understood as concerning agreement in mode of esse. But it has been shown from its own proof that this cannot be understood in that way, but only as concerning agreement of ratio. Therefore this consequent does not follow from that antecedent.

VI. For the evidence of this, it must be considered that the virtue of reason consists in this: that things assimilated to one third are also similar to one another; and likewise, things proportioned to one third are also proportioned among themselves. And therefore, since both the possible intellect and the agent intellect have a likeness and proportion with the intelligible species—the former by way of a receptive principle, the latter by way of an active principle—and since a proper act must be proportioned to its proper recipient, and a proper effect to its proper cause, the possible intellect and the agent intellect must be proportioned to one another. Accordingly, from the conformity of each intellect to the intelligible species there will be a conformity between the intellects themselves. Now each intellect conforms with the intelligible species in the same genus and the same order: because the species is both the proper act and natural act of the possible intellect, and the proper and natural effect of the agent intellect; but the proper act of any power must be of the same genus and order as that power itself, and the proper and natural effect of any agent must be of the same genus and order as its agent. To this conformity there follows a conformity in mode of being: for things of the same rational character and the same order have the same natural mode of being, as is evident upon running through all cases. It follows, then, that the intellects themselves are likewise of the same rational character and the same mode of being with respect to one another.

2. Whence, to the first doubt, it is said that the first part of the antecedent is understood of a conformity in the same generic ratio and in the same order; consequently also in the same natural mode of being. For although the specific ratio of the agent intellect is one thing and that of the intelligible species another, they nevertheless agree in this ratio and in this order, namely that they are the proper principle of intellection, and they have the same mode of being, namely immaterial esse and intellectual esse. And thus that part of the antecedent is very well proved from that proposition assumed, that every agent acts upon something like itself: namely, that every proper agent makes its natural effect of the same ratio with itself, at least generically and of the same order. For the species is the proper and natural effect of the agent intellect.

But when it is urged that that part of the antecedent cannot be understood of conformity in mode of being, because then the proof adduced would not be to the point: — it is said that indeed that argument immediately proves conformity according to reason and order: for a proper agent, containing some form only in virtuality and not formally, produces something like itself according to generic reason and in the same order. Mediate, however, it also proves conformity in mode of being. For from the fact that the form is similar to the agent intellect in genus and in the order of things, it follows that it has the same mode of being as itself.

3. To the second doubt, likewise, it is answered that the consequent is understood with respect to proportion, and according to the same reason and order, and according to the same mode of being.

For the confirmation of the first part, it has already been shown that the antecedent is also understood with respect to proportion according to reason and order.

For the approval of the second part, likewise it is evident that the antecedent concerning agreement must also be understood as agreement in mode of being, and not merely as agreement according to reason.

VII. Third, it is argued. Material forms are received in prime matter not only through the action of a separate substance, but through the action of a form of the same kind, namely one that is in matter. Therefore, by parity of reasoning, if the possible intellect is a part of the soul and not a separate substance, the agent intellect, through whose action intelligible species are made in it, will not be a separate substance but a power of the soul. — The antecedent is proved by the example of this flesh, which is generated through a form that is in those fleshes and in these bones: as is clear from Aristotle, Metaphysics VII, text 28. — But the consequence is proved thus: because just as prime matter is perfected by material forms, so the possible intellect is perfected by species understood in act.

Note that when it is said here that natural forms are received in matter not through the action of some separate substance alone, this is added for that reason only, because Aristotle, according to whose opinion Saint Thomas is arguing here, does not deny that separate substances are causes of material forms, since he holds them to be the movers of the spheres, from whose motions there is generation and corruption in lower things; but he denies that they are the sole causes of the said forms, as Plato and Avicenna wished. For besides separate substances, proper and particular material agents are required, as is shown in Metaphysics VII.

Fourth. If the intellect were separate, then either no difference or only a small one would exist between this opinion and the Platonic one. But Aristotle rejects the Platonic opinion in Metaphysics I. Therefore, etc. — The consequence is proved: because Plato held that knowledge is caused in us by the Ideas, which he posited as separate substances. Similarly, since the agent intellect is the first and principal principle of our knowledge, if it is posited as a separate substance, it is posited that knowledge is caused in us by a separate substance.

VIII. Fifth. It will follow that either we always understand, or that it is not in our power to understand in act. — The consequence is proved. Because we understand in act when the phantasms are made actually intelligible. But if the agent intellect is a separate substance, its action, which is to make phantasms actually intelligible, must either be continuous and unbroken, or else not be continuous and be interrupted at our discretion.

Sixth ⁸ It would follow that both the learned and the unlearned understand alike. — The consequence is proved: because the comparison of a separate substance to all phantasms, in whatever they may be, is one; just as the comparison of the sun is one to all heats ⁹ But the same phantasms are in them, since they sense sensible things alike.

Note that the comparison of the separate substance to all phantasms is said here to be one, because it is of the same character—namely, because it is related to all of them in the same way, being no more illuminative of one phantasm than of another: just as the sun is related in the same way to all heats, being no more the cause of one than of another.

IX. To these two arguments one could reply at once that the agent intellect always acts as far as it is able; but phantasms are not always actually intelligible, but only when they are actually disposed by the act of the cogitative power, whose use is within our control. And so to the first of these, the consequence by which it is inferred that understanding will not be within our control is denied. — To the second, the consequence is likewise denied: for not all understand those things whose phantasms they possess because not all have an act of the cogitative power suited to them.

2. Against this response, that it is not entirely sufficient, although it has some appearance of plausibility, Saint Thomas argues, because this disposition which is made by the cogitative power for the sake of understanding is either a disposition of the possible intellect for receiving intelligible forms, as Avicenna held: or it is a disposition of the phantasms so that they become actually intelligible, as Averroes and Alexander held.

If first, it is argued against. Then, because that whose nature is to receive some form does not need another disposition toward that form ¹⁰, unless perhaps contrary dispositions are present in it. Now the possible intellect by its nature is in potency to actually intelligible species, to which it is related as the diaphanous to light or to the species of color. And there is nothing in it contrary that would impede the reception of an intelligible species: for falsity, which occurs in the judgment of the intellect composing and dividing, arises not because there are certain things understood in the intellect, but from the fact that certain things are lacking to it ¹¹. — Then, because the comparison of phantasms to the possible intellect would not be as that of colors to sight, as Aristotle willed. For colors, made actually visible by light, certainly imprint their likeness in the diaphanous and in sight; which does not befit the illuminated phantasm, according to this response. — Then, because neither phantasms nor senses would be necessary per se for understanding, namely as active and causative principles of knowledge, but only per accidens, as it were preparing and rousing the possible intellect to receive; and this is the Platonic opinion, and against the order of the generation of knowledge and intellect ¹² laid down by Aristotle in I Metaphysics and II Posterior Analytics. — Saint Thomas indeed adds that this position of Avicenna accords with what he says about the generation of natural things, when he holds that natural agents only prepare matter to receive forms from a separate intelligence.

But if the second is said, then this seems to accord with the position of those who say that inferior agents dispose only toward the ultimate perfection, while the ultimate perfection is from a separate agent. This is against the opinion of Aristotle, Metaphysics VII.

X. Concerning that proposition, "That in whose nature it is to receive some form does not need a further disposition for that form," there is doubt. For then it follows that matter could immediately receive any substantial form whatsoever without any disposition, since by its nature it is in potency to every substantial form. But this seems false: because the soul cannot be received in matter unless the latter is first organized and disposed.

It also seems to be against the doctrine of St. Thomas, Prima, q. LXXVI, a. 6, where he says that prime matter is in potency to all acts according to a certain order: and thus it seems that a later form cannot be received unless it is disposed and prepared by the preceding form; just as it cannot receive the intellectual soul unless the sensitive and vegetative soul precede in it.

2. For the clarification of this point, it must be considered that St. Thomas takes esse, which by its nature is in potency to a form—or that esse whose nature it is to receive some form—to mean esse which is of itself and by its own nature disposed to receive that form. Such esse clearly does not need any further disposition for that form: for it involves a contradiction that something should be disposed by its own nature to a form and yet stand in need of a further disposition to it; for if it needed a superadded disposition, it would no longer be disposed by its own nature. Thus actually diaphanous matter, because it is of itself disposed to receive the species of color, does not need any other disposition for that species. And likewise the possible intellect, because it is disposed by its own nature to the intelligible species; on account of which it is related to that species as the diaphanous is to light, if the diaphanous be taken in potency, or as the diaphanous is to the species of color, if the diaphanous be taken in act; therefore it needs no other disposition for receiving it. And upon this the argument of St. Thomas is founded.

3. To the argument on the opposite side it is answered that we can speak in two ways of the immediate reception of a form into matter. In one way, so that that immediacy excludes a disposition preceding the form in matter by duration and ceasing at the advent of the form itself: so that the sense is that matter does not need to be disposed beforehand in duration before it receives the form, but is of itself disposed to every form. — And then the consequence is denied. For matter is immediate only to the forms of the elements, as is said below, chapter LXXXIX, and II Sentences, d. XII, a. 4: for it does not need, of itself, to be disposed by another preceding form to the form of an element; although per accidens it must be disposed to the form of one element if there happen to be in the matter dispositions contrary to the dispositions of the form to be introduced. But it does indeed need, as is said in the places cited above, to be disposed to other forms through the reception of preceding forms: as happens in the generation of man, because between matter and the intellectual soul many forms intervene. — To the proof of the consequence, however, the assumption is denied. For, according to the sense given to the proposition of St. Thomas, matter is not by its nature in potency to every form, that is, sufficiently disposed of itself and from its own nature to every form: but only to the elemental forms.

4. In another way, so that that immediacy excludes a disposition remaining in the matter together with the form itself: the sense being that between matter and form no disposition superadded to the matter intervenes, but the substantial form itself inheres immediately in the matter. And then it is said, in accordance with what was determined above ¹³, that we can speak of substantial form in two ways: in one way, as it gives corporeal substantial esse; in another way, as it gives some grade of being above corporeal esse, for instance vegetative esse, sensitive esse, or intellective esse.

If it is considered in the first way, then matter, taken in its bare state, is by its nature disposed to the reception of any substantial form whatsoever, and it does not need any other disposition for that form, as was shown above ¹⁴; and this is held from the doctrine of St. Thomas in the Prima Pars, q. LXXVI, a. 6, De Spiritualibus, art. 3, and De Anima, art. 9: but it receives every substantial form immediately. Hence the falsity of the consequent is denied. — To the first proof of this it is said that what was assumed is false concerning the soul insofar as it gives corporeal esse. For thus its perfectible subject is prime matter, not an organized body. — To the second proof it is said, in accordance with what is found in the Quaestio de Anima, the article cited above, ad 9, that matter is said to be in potency to all acts according to a certain order, not as if it received diverse forms successively, namely forms that would remain in matter, as though one disposition were ordered to another; but because what belongs to the higher form is not received except through that which belongs to the lower form. For matter is not of itself disposed to the degree of the higher form, but only to corporeal substantial esse, as was shown above ¹⁵; and through the lower degree it is disposed to the higher and more perfect degree, both proceeding nevertheless from the same form.

If, however, it is considered in the second way, then matter is not immediately receptive of every form if considered bare: but in order that it may receive a form according to a more perfect degree, there must be pre-understood in it, in the order of nature and intellect, the lower degree, as a disposition of matter toward the higher degree. — Hence, when form is likewise so considered, both the consequence and the assumption offered for its proof are false.

XI. Concerning that proof, assumed in the same argument ¹⁶, for excluding the objection by which someone might say that there is in the intellect something contrary to the intelligible form, because falsity is in the intellect, which is contrary to truth — concerning this proof, I say, it must be noted that falsity, which occurs in the judgment of the intellect composing and dividing, arises not from the fact that certain intelligibles are in the possible intellect, but from the fact that certain things are lacking to it. In the intellect of intelligibles, since the species of contraries are not contraries, as St. Thomas adduces from the mind of Aristotle, Metaphysics VI ¹⁷, text 23 — indeed one is the reason for knowing the other — but contrariety is found in it only according to truth and falsity, insofar as the opinions of contradictories, of which one is true and the other false, are contraries. Hence the contrariety found in the intellect is only a contrariety of enunciations, which presuppose species in the intellect from which the intellect proceeds to enunciate; but it is not a contrariety of things presupposed for the act of understanding. And therefore St. Thomas rightly says that falsity is not in the intellect from the fact that certain intelligibles are in it, that is: the false existing in the intellect, which is contrary to the true, is not any intelligible species, so that it would have to be removed in order for the intellect to receive another species, just as the form of water must be removed from matter, together with the qualities consequent upon it, if the form of fire is to be introduced into the matter of water. Rather, the defect and privation of some species, or of some other requisite for the intellect to make a true composition, is the reason why the intellect judges falsely and composes falsely: as when judging man to be risible, which is false, he judges thus either because he does not have the intelligible species of man or of risible, or because according to those species he cannot judge rightly, on account of a defect of the sensitive powers, whose operation the intellect needs in order to understand.

XII. Seventh ¹⁸ the principal argument runs as follows. Understanding is the noblest effect found among these lower things. Therefore it does not suffice, in order to account for it, to posit a remote agent that is a separate substance, but one must also posit a proximate agent of its own kind. Therefore, and so on. — The consequence is proved. Because the nobler effects among these lower things, beyond the higher agents, require agents of their own kind: as is evident in perfect animals.

Saint Thomas adds, however, that this argument does not proceed against Avicenna, because he holds that every animal can be generated without seed.

Concerning this proposition, "Understanding is the noblest effect in these lower things," it must be noted that the name "effect" is taken here as extending not only to that which is produced by an action, but also to the operation itself. Now understanding is said to be the noblest effect, not in respect of its entity considered absolutely and simply, because every substance is nobler than it, since every substance is nobler than every accident, speaking simply; but in respect of its mode of being, and in the character of a work and effect; for it has immaterial esse, and proceeds from the soul insofar as the soul exceeds the capacity of matter, inasmuch as it has this from being the most excellent of forms. And just as an operation takes its species from the principle of the operation, as is said in Verit., q. 20, 1, ad 2, so too does it derive its nobility from that principle.

XIII. But this argument does not seem to be effective, for two reasons. First, because someone could say that, besides the universal and remote agent, there is a proximate agent of intellection, namely the possible intellect, which, after it has received the species from the separate substance, produces intellection. And thus it is not necessary to posit the agent intellect as part of the soul.

Second, because if that proposition is universally true—that to all the nobler effects in these lower things, apart from universal agents, there must be assigned a proper agent of the same genus—then, since the intellectual soul is the noblest effect found in those lower things, it will be necessary, apart from the universal agent, which is God, to assign to it a proper agent of the same genus, namely an intellectual soul. And thus it will not be from God alone by creation, but one soul will be from another, just as one horse is generated from another. Which is against all philosophy and theology.

2. Beginning with the second, upon whose solution the solution of the first depends, it is said first that by "effect" in these lower things Saint Thomas does not understand everything produced by another in whatever way, but what is produced by a universal cause, to which it is not repugnant that it be produced also by a particular agent of its own kind. For of such effects it is true that the nobler among them are produced not only by agents of a higher order, but also require agents of their own order. Now, the intellectual soul is not such an effect, because it cannot be produced except by creation, as Saint Thomas shows in the Prima, q. 90, a. 2; but to create belongs to God alone, as was shown above ¹⁹ Therefore the objection is not to the point. — But understanding is indeed among those effects to which it is not repugnant to have a proper agent of their own order. Hence it is right that he should assign to it, besides the separate substances, a proper agent of its own kind, namely one belonging to the lower things as a power of the human soul, just as our understanding belongs to the human soul as an act received in it naturally.

It is said secondly that, although one soul is not produced by another, man nevertheless causes the soul itself to be united to matter, and thus he is the cause of its union with matter.

3. To the first objection, it is accordingly replied that it does not suffice to posit the possible intellect as its own proper agent. First, because the possible intellect is not an active but a passive power, which needs to be perfected by some agent in order to elicit intellection. — Second, because our act of understanding co-requires the making of things actually intelligible: since our soul is united to the body for this very reason, that through the senses it may receive knowledge of material things, making, by abstraction from material conditions, things intelligible in potency to be actually intelligible. But this the possible intellect cannot do, since it is a passive power. Therefore, besides the possible intellect, by which the soul can become all things, there must be in the soul an agent intellect, by which it can make all material things actually intelligible ²⁰. Hence St. Thomas says in the De Anima, art. 4, ad 8, that the act of the possible intellect is to receive intelligibles, while the action of the agent intellect is to abstract intelligibles; and that for a single act of understanding both of these actions must concur.

XIV. Eighth. To abstract universal forms from phantasms is in our intention, not only in the intention of the remote agent. Therefore there must be in us a proximate principle of such an effect, which is the agent intellect. — The consequence is proved. Because the intention of an effect demonstrates its agent. For those things that are within the intention of a higher nature alone are produced by a higher nature alone: as things generated from putrefaction, which Aristotle says come about by chance, namely by comparison with a lower nature. But those things that are intended by a lower nature are also produced by a lower nature: as animals generated from seed.

Concerning this proposition, "The intention of an effect demonstrates the agent," it must be noted that to intend belongs properly with respect to an end. Therefore, to intend some effect, namely as one's proper effect, is nothing other than to tend and be inclined toward it as toward an end and the terminus of one's operation. Now it is clear that this does not befit anything except what has within itself a productive principle of that effect. Hence it is well said that the intention of an effect demonstrates the agent: that is, that something is intended by some nature as its effect demonstrates that nature to be productive of it; for it would not be inclined toward that effect to be produced by itself unless it had within itself the principle productive of it. And this according to the condition of the intention. For if it is inclined to produce the effect immediately, then it must have in itself the proximate principle of that effect, as was said of the human soul with respect to the abstraction of universals; for experience shows that we strive toward the consideration of universals without material conditions, which is to abstract universals from particulars. But if it intends the effect as to be produced remotely by itself, it must have in itself the remote principle of that effect.

Note that this argument is the one Saint Thomas gives in the First Part, q. 79, a. 4. But from the perfection of the act of understanding he deduces only that a proper cause must be assigned to it. That other argument, however, further reasons from the perfection of the intellective soul that such a power must exist in the soul itself; as if arguing further that, if there must be in lower nature a proper power productive of the act of understanding, it is necessary that this be in the human soul, because the noblest effect must have the noblest cause; and nothing among these lower things is nobler than the human soul.

XV. Ninth. Man is the most perfect among all lower moving things. And his proper and natural operation is to understand. Therefore there must be in him a sufficient principle for understanding. Therefore in him are the agent intellect and the possible intellect. — The first inference is proved: because in the nature of anything that moves there is a principle sufficient for its natural operation, whether it consists in action or in passion. — The second is also proved: because understanding is not completed without a passion, by which the possible intellect is acted upon by the intelligible; nor without an action, by which the agent intellect makes things intelligible in act.

Tenth. It follows that understanding is not an operation proper and natural to man. And thus man cannot be defined by the fact that he is intellectual and rational. — The consequence is proved. For an operation which man exercises solely by the power of a supernatural substance is a supernatural operation, as to work miracles and to prophesy. But it is evident that if the agent intellect, without whose power man cannot understand, is a separate substance, this is above the nature of man. Therefore etc.

Note that something is done by supernatural power alone when, above the natural power of the agent, there is given to it a power for acting without which the operation could not be completed. And then that operation cannot be called natural to the agent, since it does not proceed completely and sufficiently from the power of such an agent. Therefore it follows most fittingly, as Saint Thomas deduces, that understanding will be an operation supernatural to man, if the agent intellect is a separate substance. For understanding will not then be produced by man through his natural power completely and sufficiently, but the work will be by a power superadded to his natural power.

XVI. Eleventh. Man abstracts species from phantasms and receives things actually intelligible in the mind. Of these, the first pertains to the agent intellect; the second, however, to the possible intellect. Therefore the agent intellect and the possible intellect must be powers existing formally in us. — The antecedent is proved: because we would not otherwise have come to knowledge of these actions unless we experienced them in ourselves. — The consequence is also proved: because nothing acts, as is clear from II de Anima, except through some power that exists formally in it.

Saint Thomas also used this reasoning above ²¹ to prove that the possible intellect exists in us formally, and it is there explained most fully. Therefore we need not dwell on it here.

If it is said, as Averroes says, that these actions are attributed to man insofar as these intellects are conjoined to us: it is indeed evident from what precedes, concerning the possible intellect, that its conjunction with us does not suffice for us to understand through it. But it is also argued concerning the agent intellect that it does not suffice for us to perform the operation of the agent intellect. For the forms of an art do not follow upon the action of the art, but only its formal likeness; and consequently neither can their subject, by means of those forms, produce the action of the craftsman. Therefore neither can man, by the fact that intelligible species made by the agent intellect exist in him, perform the operation of the agent intellect. — The consequence is proved. Because, according to Aristotle's example in Book III of De Anima, the agent intellect is compared to the intelligible species as art is compared to artificial forms.

2. Concerning this proposition, the forms of art do not follow the action of art, but only the formal likeness, it must be considered that for a form to follow the action of its formal productive principle, as this is understood here, is for it to be assimilated to that formal principle in its power of acting, so that it can produce that action which its formal principle can bring about. Now forms produced by nature and forms produced by art differ in this respect: forms produced by nature are assimilated to the productive form not only according to formal ratio but also with respect to mode of being; for the form of the fire producing and the form of the fire produced have the same mode of being. And therefore the action that follows from the form of the producer also follows from the form produced: because things of the same ratio and the same mode of being have the same operations; just as the form of the producing fire heats and dries, so does the form of the fire produced. But forms produced by art, although they are assimilated to art according to a formal likeness, inasmuch as they are of the same ratio with it, are nevertheless not assimilated to it according to mode of being: since art has an immaterial and intellectual esse, while a form produced by art has material esse. And therefore the operation of art need not belong to the form produced by art: for just as the art of house-building is the formal principle by which the craftsman produces a house, so the form of the house produced in matter is not the formal principle by which one house produces another. The reason for this is that this operation does not accompany the form of art according to its material esse, but only insofar as it has an immaterial and intelligible esse; and this esse does not belong to the form of art as it is in matter. Therefore Saint Thomas rightly says that the form of art does not follow the action of art, but only the formal likeness, that is, it is not assimilated to art in operating, but only in formal ratio.

XVII. Finally, the principal argument is made. If the agent intellect is a separate substance, it follows that man is not the agent of himself, but is in act through another. And thus he will not be master of his own operations; and he will not merit praise or blame; and thus moral science and civil life will perish. — The consequence is proved. Because that which cannot issue into its own operation except by being moved by an external principle is acted upon toward operating more than it acts of itself: as is evident in irrational animals, which, moved by exterior sensible things through the motion of the senses in a certain order, are acted upon more than they act of themselves. But understanding is man's proper operation, whose principal principle is the agent intellect, which makes the intelligible species in act, by which the possible intellect is in a certain way moved: that is, by formal motion, which is the actualization of what receives.

XVIII. Two doubts arise concerning this argument. The first is that, if the brutes are denied acting upon themselves toward operation because they cannot operate unless moved by an exterior principle, which is the sensible object itself, then by the same reasoning, even if the agent intellect is granted to exist in man, it will follow that man is acted upon so as to operate: for he cannot perform any operation following upon cognition unless he is moved by an exterior sensible object. And thus this argument will be no more against those who hold that intellect is a separate substance than against those who hold that it is a part of the soul.

The second reason is that, even if the agent intellect is posited in the soul, it acts of necessity: for it cannot fail to illuminate the phantasms prepared for it. And thus it will follow, even given that it is in us, that man does not act upon himself, but only receives from the giver of the agent intellect its natural inclination to illuminate the phantasms—just as other natural things are said to be moved by the giver of the form by which they are naturally inclined to motion. And so the same conclusion follows as before.

XIX. For the clarification of these points, it must be known that, since being moved to operation and having dominion over one's own operations are here taken as the same thing; and since having dominion over one's own operations is to operate voluntarily, which is to operate with that freedom by which the agent can operate or not operate: in order to see how it follows that man does not move himself to operating if the intellect is a separate substance, we must see how from that it follows that man does not have it in his power to operate and not to operate. It must be known, therefore, from the teaching of Saint Thomas in I IIae, q. vi ²², that for something to have in its power to operate and not to operate, three things are required: first, that it have in itself the principle of its own operation; second, that it have knowledge of the end; third, that it know the reason of the end and the proportion of what is ordered to the end. And therefore whichever of these is lacking in anything, that thing does not have in its power to operate and not to operate. By the principle of an operation we understand its principal principle. For in order that something have in its power to operate and not to operate, it is not enough that it have any principle whatsoever of its own operation within itself: because if it does not have the principal principle within itself, its operating must necessarily depend on another, and consequently it does not have in its power to operate and not to operate. And if its proper operation—that is, the one belonging to it insofar as it is such—does not proceed from a principal intrinsic principle of it, it is absolutely true to say that it does not move itself to operating, but is acted upon. Hence, since understanding is the proper operation of man, as befitting him insofar as he is man, and that by which the will is moved, which is the principle of motion in man; and since the agent intellect is its principal principle, as it were making the intelligible species by which the possible intellect is in act, so that it may elicit intellection: it follows that, if the agent intellect is not intrinsic to man but is a substance extrinsic to him, understanding is not in man's power; and consequently that absolutely and universally man is not the master of his own operations, but is acted upon like brute animals.

2. To the first doubt, therefore, it is said that the account is not the same of man if an agent intellect is posited in him, and if a separate substance is posited. For external sensible things are not the principal agent with respect to the operation of man insofar as he is man, as they are the principal mover with respect to brutes, but the agent intellect is. For phantasms caused by sensible things do not imprint of themselves and principally upon the possible intellect, as they imprint of themselves upon the powers of brute animals: rather, they are instruments of the agent intellect. Therefore, if the agent intellect is a substance separate from man, man's proper operation could not be brought about by man without an extrinsic principal principle, and consequently it would not be within man's power. But if it is a power existing in the soul, such an operation will be from an intrinsic principal principle, with the other conditions required. And consequently man will be master of that operation, and of the others that depend upon it.

3. To the second doubt it is answered, and it is said first that, although the agent intellect necessarily acts upon prepared phantasms, it does not follow that man is not master of his own act, and consequently of the others. For with this natural operation of the agent intellect it is compatible that man have the act of understanding freely: just as, although the will naturally inclines toward the end considered under the common aspect, nevertheless it freely wills those things that are ordered to the end; and although the intellect naturally assents to first principles, nevertheless it does not assent to the others by nature. So too, although the agent intellect naturally makes phantasms actually intelligible, nevertheless the very act of understanding will be free, as proceeding from an intrinsic principal principle with knowledge of the end and of the order of those things that are ordered to the end. But it would not be so if the agent intellect were posited to be a separate substance: for then understanding would be from an extrinsic principle as from a principal principle.

It is said secondly that, although the agent intellect, as far as it is concerned, operates naturally, nevertheless its operation is in some way voluntary, inasmuch as man voluntarily thinks and disposes the phantasms so that they become actually intelligible. Nor did Saint Thomas deny this, arguing against the response of Averroes above ²³ But he argued that that response fell into the opinion of those who say that the lower agents dispose only toward the ultimate perfection, while the ultimate perfection itself comes from a separate agent, if the agent intellect is posited to be a separate substance. This, however, does not follow if we posit the agent intellect to be a power of the soul, and consequently intrinsic to man.