Article 5 — Whether there is one separately existing agent intellect for all men

Fifth, it is asked whether there is one separately existing agent intellect for all men. (Parallel texts: ST I.79.4, 5; SCG II.76, 78; In II Sent., d. 17, q. 2, a. 1; On Spiritual Creatures, a. 10; Commentary on Aristotle’s On the Soul, bk. 3, lect. 10; Compendium theologiae, bk. 1, ch. 86; On Truth, q. 10, a. 6.)

Obj. 1: It seems that there is. For the Philosopher says in On the Soul 3 that the agent intellect is not at one time knowing and at another not. (Aristotle, On the Soul 3.5, 430a22; cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 4; Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 20.) But nothing of this nature exists in us. Hence, the agent intellect exists apart from men and, therefore, is one and the same for all men. (Cf. ST I.79.4, obj. 2; On Spiritual Creatures, a. 10, obj. 3.)

Obj. 2: Further, nothing can be in potency and in act with respect to the same thing simultaneously. Now the potential intellect is in potency with respect to every intelligible species. However, the agent intellect is in act with respect to them because it is the act producing them. Therefore, it seems that the possible and agent intellect cannot be rooted in the same substance of the soul. Hence, since the potential intellect is rooted in the essence of the soul, as is evident from the preceding articles, (Above: qq. 1–3.) the agent intellect will exist apart from the soul. (Cf. ST I.79.4, obj. 4; Compendium theologiae, bk. 1, ch. 88; Commentary on Aristotle’s On the Soul, bk. 3, lect. 4, n. 737.)

Obj. 3: But it might be said that the potential intellect is in potency to intelligible species, and the agent intellect in act with respect to them according to different modes of existence.

On the contrary, the potential intellect is not in potency to intelligible species when it possesses them, because then it is actuated by them. Hence, it is in potency to intelligible species as existing in phantasms. But the agent intellect is related to such species as the act which produces them because it makes them actually intelligible by abstraction. Hence, the potential intellect is in potency to intelligible species with respect to that mode of existence according to which the agent intellect is related to them as the one producing them.

Obj. 4: Further, in On the Soul 3 the Philosopher attributes to the agent intellect certain properties which seem to belong only to separate substances. For he says that this alone is perpetual, incorruptible, and separate. (Aristotle, On the Soul 3.5, 430a17; 430a23; cf. ST I.79.5, obj. 1; Aquinas, On Spiritual Creatures, a. 10, obj. 2.) Therefore, it seems that the agent intellect is a separate substance.

Obj. 5: Further, the intellect does not depend on any bodily disposition, because it is not united to a bodily organ. But our faculty of understanding is affected by different physical dispositions. (Aristotle, On the Soul 2.9, 421a25–26; cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 19.) Consequently, this faculty of ours is not identical with this intellect which is present in us, and it seems that the agent intellect has a separate existence.

Obj. 6: Further, in order to have activity, an agent and a patient alone are necessary. Therefore, if the potential intellect, which is the patient in cognition, is a part of our substantial principle, as was previously shown, (Above: q. 3.) and the agent intellect is also a part of our soul, it seems that we possess within ourselves everything necessary in order that we may be able to understand. Hence, we require nothing more in order to be able to do so. But this is clearly false. For we need the senses through which we acquire the experience necessary for cognition. (Cf. Aristotle, Posterior Analytics 2.19, 100a3–4; Metaphysics 1.1, 981a1–2; Aquinas, Commentary on Aristotle’s Posterior Analytics, bk. 2, lect. 20; Commentary on Aristotle’s Metaphysics, bk. 1, lect. 1, nn. 15–16.) This is the reason why a man deprived of a sense, for instance sight, lacks a knowledge of colors. (Cf. Aristotle, Posterior Analytics 1.18, 81a38–39; Aquinas, On Truth, q. 10, a. 6, s.c.; ST I.78.4, obj. 4.) In order to learn, we also require instruction, which is given by a teacher. (Cf. Aristotle, Posterior Analytics 1.1, 71a1–2; Aquinas, On Truth, q. 11, a. 2, resp.) And above all, we stand in need of the illumination given by God, for it is said, the true Light that enlightens every man was coming into this world (John 1:9). (Cf. Aquinas, On Spiritual Creatures, a. 10, obj. 1; ST I.79.4, obj. 1 and 3.)

Obj. 7: Further, the agent intellect is related to intelligible objects as light is to visible objects, as is evident in On the Soul 3. (Aristotle, On the Soul 3.5, 430a14–16.) But one light existing apart from things, that is, the sun, suffices to make all things actually visible. Consequently, one intellectual light existing apart from men suffices to make everything actually intelligible. Hence, it is unnecessary to maintain that an agent intellect exists in each one of us.

Obj. 8: Further, the agent intellect is similar to an art, as is clear in On the Soul. (Aristotle, On the Soul 3.5, 430a12–15.) But an art is a principle separate from the objects produced by it. Therefore, the agent intellect is also a separate principle. (Cf. Aquinas, On Spiritual Creatures*, a. 10, obj. 11.)*

Obj. 9: The perfection of a nature consists in being like its agent, for a thing generated is perfect when it resembles the thing producing it. (Cf. Aristotle, On the Soul 2.4, 415a26–b3.) A thing produced by art is also perfect when it resembles the form in the mind of the artisan. Therefore, if the agent intellect belongs to our soul, the ultimate perfection and happiness of our soul will be found in some part of the soul itself, which is evidently false. For in that case the ultimate happiness of the soul would be the enjoyment of itself. Consequently, the agent intellect is not something that exists within ourselves.

Obj. 10: Further, an agent is nobler than a patient, as is pointed out in On the Soul. (Aristotle, On the Soul 3.5, 430a17–19; cf. Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 19.) Therefore, if the potential intellect is separated in some measure from the body, the agent intellect will be separated to an even greater degree; and we see that this can be so only if the agent intellect is held to be completely separated from the substance of the soul.

On the contrary (1), there is this statement in On the Soul 3, that since there is something in every nature that is like matter and something that is productive, these two distinct elements must likewise be found within the soul. (Aristotle, On the Soul 3.5, 430a10–14.) The potential intellect corresponds to one of these, the agent intellect to the other. Therefore, both the possible and agent intellect belong to the soul.

Furthermore (2), the operation of the agent intellect is to abstract intelligible species from phantasms. Now it is certain that this operation is not continually taking place in us. However, there would be no reason why such abstraction should sometimes occur and sometimes not, as is seen to be the case if the agent intellect were a separate substance. Consequently, the agent intellect is not a separate substance.

I answer that it is obviously more reasonable to maintain that the agent intellect is unique and separate than to hold that this is true of the potential intellect. (Cf. Aquinas, On the Unity of the Intellect, ch. 4.) For the potential intellect, in virtue of which we are capable of understanding, is sometimes in potency and sometimes in act. The agent intellect, on the other hand, is that which makes us be understanding in act. Now an agent exists in separation from the things which it brings into actuality, but obviously whatever makes a thing potential is wholly within that thing. For this reason, many maintained that the agent intellect is a separate substance, and that the potential intellect is a part of our soul. (This seems to be the opinion of Avicenna.) Furthermore, they held that this agent intellect is a specific kind of separate substance, which they call an intelligence. They held that it is related to our souls, and to the entire sphere of active and passive qualities, as superior separate substances, which they also call intelligences, are related to the souls of the heavenly bodies, for they considered these to be animated, and to the heavenly bodies themselves. Hence, they maintained that, as superior bodies receive their motion from these separate substances, and the souls of the heavenly bodies their intelligible perfections, so also do all the bodies of this inferior sphere receive their forms and movements from the separate agent intellect, while our soul receives its intelligible perfections from it. (Cf. Avicenna, Metaphysics, bk. 9, ch. 4; Aquinas, In II Sent., d. 18, q. 2, a. 2, resp.; Commentary on Sense and What Is Sensed, tract. 1, ch. 9; Averroes, Commentary on Aristotle’s On the Soul, bk. 5, comm. 6.) But because the Catholic faith maintains that God is the agent operating in our souls and not some separate substance in nature, some Catholics asserted that the agent intellect is God himself, who is the true Light that enlightens every man coming into this world (John 1:9). (Cf. William of Auvergne (1180/90–1249 AD), De anima, ch. 7; see also the works of Dominic Gundisalvi (among many other Augustinians), the 12th century translator of Avicenna.)

But this position, if anyone examines it carefully, is seen to be implausible, because the superior substances are related to our souls as heavenly bodies are to inferior bodies. For, as the powers of superior bodies are certain universal active principles in relation to inferior bodies, so also the divine power and the powers of different secondary substances—if the latter do influence us in any way—are related to our souls as universal active principles. However, we see that there must exist in addition to the universal active principles of the heavenly bodies certain particular active principles which are powers of inferior bodies, limited to the proper operation of each and every one of them. This is particularly necessary in the case of perfect animals because certain imperfect animals are found for whose production the power of a heavenly body suffices, as is evident in the case of animals generated from decomposed matter. (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 7.) However, in the generation of perfect animals, a special power is also required in addition to the heavenly power, and this power is present in the seed. (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 9.) Therefore, since intellectual operation is the most perfect thing existing in the entire order of inferior bodies, we need, in addition to universal active principles—namely, the power of God enlightening us, or the powers of any other separate substance (Cf. Aquinas, On Truth, q. 11, a. 3.)—an active principle existing within us by which we are enabled to understand actually. This power is the agent intellect.

We must also consider this, that, if the agent intellect is held to exist as a separate substance along with God, a consequence repugnant to our faith will follow, (Cf. Aquinas, In II Sent., d. 18, q. 2, resp.; On Spiritual Creatures, a. 10, resp.) namely, that our ultimate perfection and happiness consists not in a certain union of our soul with God, as the Gospel teaches, saying, this is eternal life, that they know thee, the only true God (John 17:3), but with some other separate substance. (Averroes, Commentary on Aristotle’s On the Soul, bk. 5, comm. 6.) For it is evident that man’s ultimate beatitude or happiness depends upon his noblest operation, understanding, which operation, in order to be fully completed, requires the union of our intellect (See Aristotle, Nicomachean Ethics 10.7, 1177a12–16; Aquinas, Commentary on the Nicomachean Ethics, bk. 10, lect. 10.) with its active principle. For, indeed, anything passive in any way whatever is perfected only when joined with the proper active principle which is the cause of its perfection. (Cf. Aquinas, On Spiritual Creatures, a. 10, resp.) Therefore, those maintaining that the agent intellect is a substance existing apart from matter say that man’s ultimate happiness consists in being able to know the agent intellect.

Moreover, if we give the matter further careful consideration, we will find that the agent intellect cannot be a separate substance for the same reason that the potential intellect cannot be, as was shown above. (Above: qq. 1–3.) For, as the operation of the potential intellect consists in receiving intelligible species, so also does the proper operation of the agent intellect consist in abstracting them, for it makes them actually intelligible in this way. Now we experience both of these operations in ourselves because we receive our intelligible species and abstract them as well. (Cf. ST I.79.4, resp.; On Spiritual Creatures, a. 10, resp.; Commentary on Aristotle’s On the Soul, bk. 3, lect. 4; Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 18, 36.) However, in anything that operates there must be some formal principle whereby it operates formally, because a thing cannot operate formally through something that possesses existence distinct from itself. But, although the motive principle of an activity is separate from the thing which it causes, nevertheless there must be some intrinsic principle whereby a thing operates formally, whether it be a form or some sort of impression. Therefore, there must exist within us a formal principle through which we receive intelligible species, and one whereby we abstract them. These principles are called the possible and the agent intellect, respectively. Consequently, each exists within us. Moreover, the formal intrinsic existence in us of the agent intellect is not accounted for simply by the fact that the action of the agent intellect, namely, the abstracting of intelligible species, is carried out through phantasms illumined in us by its action. For every object produced by art is the effect of the action of an artificer, the agent intellect being related to the phantasms illumined by it as an artificer is to the things made by his art. (Cf. Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 5, 36; Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 4.)

Now it is not difficult to see how both of these can be present in one and the same substance of the soul, that is, the potential intellect, which is in potency to all intelligible objects, and the agent intellect which makes them actually intelligible; (Cf. Aquinas, In II Sent., d. 17, q. 2, a. 1, resp.; SCG II.77; Compendium theologiae, bk. 1, ch. 88; ST I.79.4, ad 4; Commentary on Aristotle’s On the Soul, bk. 3, lect. 4; On Spiritual Creatures, a. 10, ad 4.) because it is not impossible for a thing to be in potency and in act with respect to one and the same thing in different ways. Therefore, if we consider the phantasms themselves in relation to the human soul, in one respect they are found to be in potency, inasmuch as they are not abstracted from individuating conditions, although capable of being abstracted. In another respect they are found to be in act in relation to the soul, namely, inasmuch as they are likenesses of determinate things. Therefore, potentiality with respect to phantasms must be found within our soul so far as these phantasms are representative of determinate things. This belongs to the potential intellect, which is, by its very nature, in potency to all intelligible objects, but is actuated by this or that object through species abstracted from phantasms. Our soul must also possess some active immaterial power that abstracts the phantasms themselves from material individuating conditions. This belongs to the agent intellect, so that it is, as it were, a power participated from the superior substance, God. Hence, the Philosopher says that the agent intellect is like a certain habit and light. (Aristotle, On the Soul 3.5, 430a14–15.) In the Psalms it is also said, lift up the light of thy countenance upon us, O Lord (Ps 4:6 [7]). Something resembling this in a certain degree is apparent in animals who see by night. (Cf. Aquinas, On Spiritual Creatures, a. 10, ad 4.) The pupils of their eyes are in potency to every color inasmuch as they have no one determinate color actually but make colors actually visible in some way by means of a certain innate light. (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 15.)

Indeed, some men thought that the agent intellect does not differ from our habit of indemonstrable principles. (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 4.) But this cannot be the case, because we certainly know indemonstrable principles by abstracting them from singulars, as the Philosopher teaches in Posterior Analytics 2. (Aristotle, Posterior Analytics 2.19, 100a15–b5.) Consequently, the agent intellect must exist prior to the habit of first indemonstrable principles in order to be the cause of it. Indeed, the principles themselves are related to the agent intellect as certain of its instruments, because the intellect makes things actually intelligible by means of such principles.

Reply Obj. 1: The Philosopher’s statement that the intellect is not at one time knowing and at another not (Aristotle, On the Soul 3.5, 430a22.) is not understood of the agent intellect, but of the intellect-in-act. (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 4.) For after Aristotle had determined the role of the possible and agent intellect, he had to determine the role of the intellect-in-act.

He first distinguishes it in relation to the potential intellect because the potential intellect and the thing known are not one and the same. However, the intellect or science-in-act is the same as the thing actually known. Aristotle had said the same thing about sense, namely, that sense and what is potentially sensible differ from each other, but that sense and what is actually sensed are one and the same. (Aristotle, On the Soul 3.2, 425b26–27; 426b15–16.)

Second, he shows how the potential intellect is related to the intellect-in-act, because in one and the same individual, intellect in potency precedes intellect-in-act. (Aristotle, On the Soul 3.5, 430a20–21; cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 4.) However, it does not precede it absolutely, for he very often uses this manner of speaking concerning things that pass from potentiality to actuality. (Cf. Aristotle, Metaphysics 9.8, 1049b10–25.) Then he makes the statement quoted above, in which he shows the difference between the potential intellect and the intellect-in-act, because the potential intellect sometimes understands and sometimes does not, which cannot be said of the intellect-in-act. (Aristotle, On the Soul 3.5, 430a22.) He points out a similar difference in Physics 3 between causes in potency and causes in act. (Aristotle, Physics 2.3, 195a32–b6; 3.1, 201a20; cf. Aquinas, Commentary on Aristotle’s Physics, bk. 2, lect. 6, n. 191.)

Reply Obj. 2: The substance of the soul is in potency and in act with respect to the same phantasms, but not in the same way, as was shown above. (Above: resp.)

Reply Obj. 3: The potential intellect is in potency with respect to intelligible species according to the existence that such species have in phantasms; and the agent intellect is in act with respect to intelligible species according to that same existence, but for different reasons, as was shown. (Above: resp.)

Reply Obj. 4: Those words of the Philosopher, this alone is separate, immortal, and perpetual, (Aristotle, On the Soul 3.5, 430a17; 430a23.) cannot be understood to apply to the agent intellect. For Aristotle had also previously stated that the potential intellect is separate. However, they must be understood to apply to the intellect-in-act in view of the context in which they occur, as was shown above. (Above: ad 1; cf. Aristotle, On the Soul 3.5, 430a17.) For intellect-in-act embraces both the potential intellect and the agent intellect. (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 4; Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 36.) And only that part of the soul which contains the agent and potential intellects is separate, perpetual, and immortal. For the other parts of the soul have no existence without the body.

Reply Obj. 5: Diversity of dispositions causes the intellective faculty to understand more or less perfectly by reason of the powers which aid the intellect in abstracting. (Below: q. 8.) These are the powers employing corporeal organs, such as imagination, memory, and the like.

Reply Obj. 6: Although our soul possesses an agent and a potential intellect, nevertheless something extrinsic is required so that we may be able to understand. First of all, indeed, we need phantasms, derived from the senses, by means of which the likenesses of particular things are presented to the intellect. For the agent intellect is not an act in which the determinate species of all things can be received in order to be known, any more than light can cause sight to apprehend particular kinds of colors, unless those particular kinds of colors are present to sight. (Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 4.) Moreover, since we maintained above that the agent intellect is a certain power in which our souls share, as a kind of light, we must maintain that some exterior cause exists from whom such light is participated, (ST I.84.5, resp.; I.88.3, ad 1.) and we call this exterior cause, God, who teaches within us inasmuch as he infuses light of this kind into our soul. Because of his munificence, he bestows upon us, in addition to this natural light, a richer one in order that we may be able to know those things which the natural light of reason cannot attain. Such, for instance, is the light of faith (Cf. ST I.1.1, ad 2; I-II.109.1, resp.) and of prophecy. (Aquinas, On Truth, q. 12, a. 1, resp.; a. 2, ad 3; q. 11, a. 1, resp.; ST I-II.109.1, resp.; II-II.171.2, resp.; I.117.1, resp.; In II Sent., d. 9, q. 1, a. 2, ad 4; SCG II.75.)

Reply Obj. 7: The colors moving the sense of sight are outside the soul. However, the phantasms which move the potential intellect are within us. Therefore, although the exterior light of the sun is adequate for making colors actually visible, nevertheless in order that phantasms may be made actually intelligible, an interior light is required, and this is the light of the agent intellect. Furthermore, the intellective part of the soul is more perfect than the sensory. Hence, it is even more necessary that adequate principles be present to the intellect for the performance of its proper operation. For this reason, it is also a matter of experience that, by the intellective part of our soul, we both receive intelligible species and abstract them, which indicates that there exists in us intellectually not only a passive but also an active power. This is not true in the case of the senses. (Above: q. 4.)

Reply Obj. 8: Although there is a certain likeness between the agent intellect and an art, the likeness need not hold in all respects.

Reply Obj. 9: The agent intellect is not sufficient of itself to actuate completely the potential intellect, because the determinate accounts of all things do not exist in it, as has been explained. (Above: ad 6.) Therefore, to acquire complete perfection, the potential intellect needs to be united in a certain way to that agent in whom the accounts of all things exist, namely, God.

Reply Obj. 10: The agent intellect is nobler than the potential intellect because an active power is nobler than a passive power. It is also more independent of matter than the potential intellect inasmuch as it is further removed from any participation in matter. But its independence is not that of a separate substance.