Article 9 — Whether the potential intellect is one in all men

Ninth, it is asked whether the potential intellect is one in all men. (Parallel texts: In II Sent., d. 17, q. 2, a. 1; SCG II. 59, 73,75; Disputed Questions on the Soul, q. 3; Commentary on Aristotle’s On the Soul, bk. 3, lect. 1; Quodlibet III, q. 8, a. 1; Compendium theologiae, ch. 85; ST I.76.2; On the Unity of the Intellect against the Averroists, cc. 4–5.)

Obj. 1: And it would seem that it is. For Augustine says in the book On the Magnitude of the Soul, if ever I say that there are many souls, I shall be smiling at myself. (Augustine, On the Magnitude of the Soul, bk. 1, ch. 32, para. 69 (PL 32:1073; CSEL 89:217).) It seems laughable, therefore, to say that there are many intellectual souls. (Cf. ST I.76.2, obj. 6.)

Obj. 2: Furthermore, in those things which are without matter, there is one individual in one species, (Aristotle, Metaphysics 8.6, 1045a36–b7.) as has been shown. (Above: a. 8, resp.) But the potential intellect, or the intellectual soul, since it is a spiritual substance, is not composed of matter and form, as was shown before. (Above: a. 1, resp.) Therefore, there is only one intellectual soul, or potential intellect, in the whole human species. (Cf. Aquinas, Disputed Questions on the Soul, q. 3, obj. 20; ST I.76.2, obj. 1.)

Obj. 3: But it was said that even if the intellectual soul does not have matter of which it is made, nevertheless it has matter in which it exists, namely, bodies, and in consequence of the multiplication of these intellectual souls are multiplied. (Cf. Aquinas, Disputed Questions on the Soul, q. 3, obj. 13; In II Sent., d. 17, q. 2, a. 1, ad 5.)

On the contrary, when the cause is removed the effect is removed. (Cf. Peter Abelard, Dialectica, tract. 3, bk. 1, “De locis.”) If, then, the multiplication of bodies is the cause of the multiplication of souls, when the bodies are removed a multiplicity of souls cannot remain. (Cf. ST I.76.2, obj. 2.)

Obj. 4: Furthermore, individuation takes place by way of a determination of essential principles. For just as it is of the essence of man to be composed of a soul and a body, so it is of the essence of Socrates to be composed of “this particular soul” and “this particular body,” as is clear from the Philosopher in Metaphysics 7. (Aristotle, Metaphysics 7.10, 1035b28–31; cf. Aquinas, Commentary on the Metaphysics, bk. 7, lect. 10, n. 1490.) But the body is not of the essence of the soul. Therefore, it is impossible for a soul to be individuated by a body, and so souls will not be multiplied in consequence of the multiplication of bodies. (Cf. Aquinas, Disputed Questions on the Soul, q. 3, obj. 13.)

Obj. 5: Furthermore, Augustine says in Against Felicianus, if we seek the origin of the power of a living thing, the soul is prior to the mother, and it seems to have been born of her again along with the offspring, (Vigilius of Thapsus (Pseudo-Augustine, 5th cent. AD), Contra Felicianum, de unitate Trinitatis, bk. 1, ch. 12 (PL 42:1167).) and he is speaking of the soul by which the mother is animated, as he immediately adds. From this, he seems to say that there is the same soul in the mother and in the son, and for the same reason in all men.

Obj. 6: Furthermore, if the potential intellect were one thing in me and another in you, the thing that is understood would have to be one thing in me and another in you, since the thing that is understood is in the intellect; thus, the thing that is understood would have to be counted by counting individual men. But all things which are counted by counting individuals have in common a thing that is understood; thus, for a thing that is understood there will be a thing that is understood, and on to infinity, (Cf. Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 5.) which is impossible. Therefore, there is not one potential intellect in me and another in you. (Below: obj. 13.)

Obj. 7: Furthermore, if there were not one potential intellect in all men, whenever it happens that knowledge is caused in a pupil by a teacher it would have to be the case that either the numerically same knowledge which is in the teacher would flow into the pupil, or that the knowledge of the teacher would cause the knowledge of the pupil as the heat of fire causes heat in faggots, or else learning would be nothing but remembering. (Cf. Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 5; Aquinas, In III Sent., d. 33, q. 1, a. 2, qa. 1, resp.) For if a pupil has the knowledge that he learns before he learns it, learning is remembering. But if he does not have it previously, either he acquires it as something that exists previously in another, namely, in the teacher, or as something that does not exist previously in another; and in that case, it would have to be caused in him anew by another. Now, these three things are impossible. For, since knowledge is an accident, the numerically same knowledge cannot pass over from subject to subject, because, as Boethius says, accidents can be corrupted but they cannot be transmuted. (It is commonly thought that this reference is to Boethius, Commentary on the Categories, bk. 1, “De denominativis” (PL 64:173B); cf. Aquinas, In II Sent., d. 26, q. 1, a. 2, obj. 1; In IV Sent., d. 12, q. 1, a. 1, qa. 3, resp.; Disputed Questions on the Power of God, q. 3, a. 7, resp.; Moses Maimonides, The Guide for the Perplexed, bk. 1, ch. 73, comm. prop. 6.) Similarly, also, it is impossible for the knowledge of the teacher to cause knowledge in the pupil, not only because knowledge is not an active quality but also because the words which the teacher utters only stimulate the pupil to understanding, as Augustine says in the book On the Teacher. (Augustine, On the Teacher, bk. 1, ch. 12, para. 40 (CCSL 29:197–99; PL 32:1217; CSEL 77:48–50).) Moreover, the statement that learning is remembering is contrary to the Philosopher in Posterior Analytics 1. (Aristotle, Posterior Analytics 1.1, 71a27–30; 71b5–8.) Therefore, there are not different potential intellects in all men. (Cf. ST I.76.2, obj. 5.)

Obj. 8: Furthermore, every cognitive power which is in corporeal matter knows only those things which have an affinity with the matter in which it is; thus, for instance, the sight knows only colors, which have an affinity with the pupil, which is able to take on colors because of its own transparency. But the potential intellect is not able to take on only those things which have an affinity either with the whole body or with some part of it. Therefore, the potential intellect is not a cognitive power in corporeal matter, neither in the whole body nor in any part of it. Therefore, it is not multiplied in consequence of the multiplication of bodies.

Obj. 9: Furthermore, if the intellectual soul or the potential intellect is multiplied in consequence of the multiplication of bodies, this is the case only because it is the form of the body. But it cannot be the form of the body, since it is composed of matter and form, as many assert; (Above: a. 1, resp.) for a thing that is composed of matter and form cannot be the form of anything. Therefore, the intellectual soul or the potential intellect cannot be multiplied in consequence of the multiplication of bodies.

Obj. 10: Furthermore, as Cyprian says, (Cyprian of Carthage, Epistle to Magnus (PL 3:1143).) the Lord forbade his disciples to enter the city of the Samaritans (See Matthew 10:5.) on account of the sin of schism, because the ten tribes had seceded from the kingdom of David, afterwards establishing a sovereign kingdom for themselves in Samaria. Now it was the same people in the time of Christ as it had previously been. Now a people is to a people as a man is to a man and a soul is to a soul. (See below: ad 8.) Therefore, by the same reasoning, one soul is in him who lived formerly and in another who follows after; and so, through the same reasoning, the same soul will be in each individual man.

Obj. 11: Furthermore, an accident depends on its subject more than a form depends on its matter, since the form gives actual being to the matter absolutely, (Cf. Boethius, On the Trinity, ch. 2 (PL 64:1250B): omne namque esse forma fit.) whereas an accident does not give actual being to a subject absolutely. But one accident can exist in many subjects, just as there is one time in many movements, as Anselm says. (Anselm of Canterbury, On Truth, bk. 1, ch. 13 (PL 158:486C).) Therefore, much more can one soul belong to many bodies; and thus, there do not have to be many potential intellects.

Obj. 12: Furthermore, the intellectual soul is more powerful than the vegetative. But the vegetative soul is able to quicken something outside the body whose form it is; for Augustine says in On Music 6 (Augustine, On Music, bk. 6, ch. 8, para. 21 (PL 32:1174; CSEL 102).) that the sight rays are quickened by the soul of the one who sees, and are even projected far out to the thing that is seen. Therefore, much more can the intellectual soul perfect other bodies in addition to the body wherein it is.

Obj. 13: Furthermore, if the potential intellect is multiplied in consequence of the multiplication of bodies, the intelligible species, which are in the potential intellect in me and in you, must be multiplied in consequence of the multiplication of bodies. But from all forms that are multiplied in consequence of the multiplication of corporeal matter, there can be abstracted some common notion. Therefore, from the forms that are understood through the potential intellect, there can be abstracted some common notion that is understood; and by the same reasoning, since that understood notion is multiplied in consequence of the multiplication of the potential intellect, there will be an abstracting of another understood notion, on to infinity. Now this is impossible. There is, then, one potential intellect in all men. (Cf. Aquinas, In II Sent., d. 17, q. 2, a. 1, obj. 3; ST I.76.2, obj. 4; SCG II.59; Compendium theologiae, ch. 85; Disputed Questions on the Soul, q. 3, obj. 17.)

Obj. 14: Furthermore, all men agree on first principles. (Cf. ST I.84.2, resp.; Aristotle, Posterior Analytics 2.19, 99b17–100b17; Metaphysics 4.3–4.5, 1005a20–1009a38; Boethius, Hebdomads, axiom 1 (PL 64:1311B).) But this would not be the case if that whereby they know first principles were not one thing common in all men. Now, such is the potential intellect. There is, then, one potential intellect in all men. (Cf. Aquinas, Disputed Questions on the Soul, q. 3, obj. 7.)

Obj. 15: Furthermore, no form that is individuated and multiplied through matter is understood in act. But the potential intellect, whenever it actually understands, is the intellect in act, and the intellect in act is the thing that is understood in act, as is said in On the Soul 3, (Aristotle, On the Soul 3.7, 431a1; 3.4, 430a3–4; 430a19–20; Metaphysics 12.9, 1075a3–5; cf. Aquinas, Commentary on the Metaphysics, bk. 12, lect. 11, n. 2620.) just as the sense in act is the thing that is sensed in act. Therefore, the potential intellect is not individuated nor multiplied through corporeal matter; and so, it is one in all men.

Obj. 16: Furthermore, a thing that is received is in the recipient according to the mode of the recipient. But an intelligible species is received in the intellect as something understood in act and not individuated by matter; therefore, neither is it multiplied by the multiplication of corporeal matter.

Obj. 17: Furthermore, the potential intellect even of Socrates or of Plato understands its own essence, since the intellect reflects on itself; (Cf. Book of Causes, proposition 14 [15]: omnis sciens qui scit essentiam suam est rediens ad essentiam suam reditione completa, etc.; cf. Aquinas, In I Sent., d. 17, q. 1, a. 5, ad 3; In II Sent., d. 19, q. 1, a. 1, resp.) therefore, the very essence of the potential intellect is understood in act. But no form that is individuated and multiplied by matter is understood in act. Therefore, the potential intellect is not individuated and multiplied by corporeal matter; and thus, the only remaining alternative is that there is one potential intellect in all men. (Cf. Aquinas, Disputed Questions on the Soul, q. 3, obj. 22.)

On the contrary (1), there is what is said, after this I looked, and behold, a great multitude which no man could number (Rev 7:9). Now, that multitude was not composed of men living in a bodily way but of souls set free from the body. Therefore, there are many intellectual souls, not only now, merely when they are united to the body, but also when they are set free from bodies.

Furthermore (2), Augustine says in Against Felicianus, let us imagine, as many wish, that there is a universal soul in the world; (Vigilius of Thapsus (Pseudo-Augustine), Contra Felicianum, de unitate Trinitatis, bk. 1, ch. 12 (PL 42:1166–67).) and afterwards he adds, when we propose such things, let us say in advance that they are objectionable. Therefore, it is unlikely that there is one soul belonging to all men.

Furthermore (3), the intellectual soul is more closely bound to the human body than its mover is to a heavenly body. But the Commentator says in On the Soul 3 (Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 5; cf. Aristotle, On the Soul 3.4, 429a18–24; On the Heavens 1.8, 276a18–b25; 1.9, 277b27–278b8; Metaphysics 12.8, 1074a31–35.) that if there were several movable bodies there would be several movers in the heavenly spheres. All the more, therefore, since there are many human bodies, will there be many intellectual souls, and not just one potential intellect. (Cf. Aquinas, Disputed Questions on the Soul, q. 3, obj. 14.)

I answer that to make this question clear it is necessary to understand in advance what is meant by the term potential intellect and agent intellect. Now, it must be noted that Aristotle went on to a study of the intellect by way of a comparison with the senses. (Aristotle, On the Soul 3.4, 429a13–b5; cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 1.) Now, as regards the senses, since we find ourselves sometimes sensing in potency and sometimes in act, it is necessary to posit in us some sense power whereby we may be sensing in potency, and this power must be in potency to the species of sensible things, and not have any of these species actually in its own essence; otherwise, if the senses were to possess sensible things in act, as the ancient philosophers asserted, (Aristotle, On the Soul 2.5, 417a2–9.) it would follow that we would always be sensing in act. Similarly, since we find ourselves sometimes understanding in act and sometimes in potency, it is necessary to posit some power whereby we may be understanding in potency, and this power does not have in its own essence and nature any of the natures of sensible things which we can understand, but it should be in potency to all things. On this account, it is called the potential intellect, just as the sense power too, according as it is in potency, might be called the “possible sense.” Now, a sense which is in potency is reduced to act through objects that are actually sensible, which are outside the soul, and hence it is not necessary to posit an agent sense. Similarly, it would not be necessary to posit an agent intellect if the universals which are actually intelligible subsisted of themselves outside the soul, as Plato asserted. But because Aristotle asserted that these universals do not subsist except in sensible objects, which are not actually intelligible, he necessarily had to posit some power, which would make the objects that are intelligible in potency to be actually intelligible, by abstracting the species of things from matter and from individuating conditions. This power is called the agent intellect. (Aristotle, On the Soul 3.5, 430a10–17.)

Concerning the potential intellect, Averroes, in On the Soul 3 (Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 5.) asserted that there was a kind of substance separated in existence from the bodies of men, according to which it was connected with us through phantasms, and second, that there was one potential intellect for all. Now, that this assertion is contrary to faith is easy to see, for it takes away the rewards and punishments of a future life.

But it must be shown that this assertion is in itself impossible according to the true principles of philosophy. Now, it was shown above when we were discussing the union of a spiritual substance with a body that on this view it would follow that no particular man would understand anything. (Above: a. 2, resp.) But granted, for the sake of argument, that some particular man would be able to understand through an intellect that is so separated, three incongruities follow if it be asserted that there is one potential intellect for all men, whereby they all understand.

The first is that it is not possible for one power to have many actions at one and the same time with respect to the same subject. Now, it happens that two men at one and the same time may understand one and the same intelligible thing. If, then, they both understand through one potential intellect, it would follow that they both have numerically one and the same intellectual activity; thus, for instance, if two men were to see by means of a single eye, it would follow that the same act of seeing belongs to both. It is clear that this is utterly impossible. Nor can it be said that my act of understanding is different from your act of understanding by reason of the diversity of the phantasms. For a phantasm is not a thing that is understood in act, but this latter is something abstracted from it, which is held to be a word. Hence, the diversity of the phantasms is extrinsic to intellectual activity, and thus cannot cause differences in it.

The second is that it is impossible for that whereby individuals obtain their species to be numerically one in the individuals of the same species. For if two horses should agree in that numerically same reality whereby they obtained their species “horse,” it would follow that two horses are one horse, which is impossible. And on this account, it is said in Metaphysics 7 (Aristotle, Metaphysics 7.10, 1035b27–33; cf. Aquinas, Commentary on the Metaphysics, bk. 7, lect. 10, n. 1491.) that the principles of a species, once they are determinate, constitute an individual. Thus, if the essence of man is that he be composed of soul and body, it is of the essence of “this man” that he be composed of “this soul” and “this body.” Hence, the principles of every species must be multiplied in the several individuals of the same species. Now, that from which a thing obtains its species is known through some proper activity that is a consequence of the species. For we judge that to be true gold which has the proper activity of gold. The proper activity of the human species is understanding; and hence, in accordance with this activity, the Philosopher in Ethics 10 (Aristotle, Nicomachean Ethics 10.7, 1177a12–b4.) sets forth the ultimate happiness of man. The principle of this activity is not the passive intellect, that is, the cogitative power or the sense-appetite which somehow participates in reason, since these powers have no activity except through a corporeal organ, whereas the act of understanding cannot take place through a corporeal organ, as is proven in On the Soul 3. (Aristotle, On the Soul 3.4, 429a24–25.) Thus, the only remaining alternative is that the potential intellect is that whereby this particular man obtains his human species, and not the passive intellect, as Averroes imagines. (Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 5, 20, 36; below: a. 10, resp.) The only remaining alternative, therefore, is that it is impossible that there be one potential intellect in all men.

Third, it would follow that the potential intellect would not receive any species that are abstracted from our phantasms, if one intellect belongs to all those who are and who have been. For it would follow, now that many men who knew many things have already gone before us, that with respect to all those things which they knew the potential intellect would be in act and not in potency to receive them, because nothing receives what it already has. (See Aristotle, On the Soul, 3.4, 429a18–21; Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 4; cf. Aquinas, On the Unity of the Intellect against the Averroists, ch. 4.) From this it would further follow that if we are made understanding and knowing through the potential intellect, knowing in our case is nothing but remembering. And yet, too, this very thing in itself would seem incongruous: that the potential intellect, if it be a substance separated in existence, should be reduced to act through the phantasms, since the higher things among beings do not need lower things for their own perfection. For just as it would be incongruous to say that heavenly bodies are perfected in act by receiving something from lower bodies; similarly, and all the more so, it is impossible for a separated substance to be perfected in act by receiving something from phantasms.

It is also obvious that this assertion is opposed to the words of Aristotle. (Cf. Aquinas, On the Unity of the Intellect against the Averroists, ch. 1.) For when he begins his investigation of the potential intellect, right from the beginning he calls it a part of the soul, saying, now about the part of the soul whereby the soul knows and perceives. (Aristotle, On the Soul 3.4, 429a10–11.) But when he wishes to investigate the nature of the potential intellect, he passes over a certain difficulty, namely, whether the intellectual part is separable from the other parts of the soul as a subsistent thing, as Plato asserted, (Cf. Aristotle, On the Soul 1.5, 411b5–6; Averroes, Commentary on Aristotle’s On the Soul, bk. 1, comm. 90.) or mentally only. This is what he says: whether it be separable as an existing thing or inseparable spatially but mentally. (Aristotle, On the Soul 3.4, 429a11–12.)

From this it is clear that whichever of these assertions is made, the opinion which he had in mind concerning the potential intellect will still hold good. But it would not hold good that the potential intellect is separated only mentally, if the assertion that was mentioned before were a true one. Hence, the opinion that was mentioned before is not the view of Aristotle. Afterwards, he also adds that the potential intellect is that whereby the soul forms opinions and understands, (Aristotle, On the Soul 3.4, 429a23.) and many other things of this kind; (Aristotle, On the Soul 3.4, 429a10–b5.) and from these statements he manifestly gives us to understand that the potential intellect is something belonging to the soul and is not a separated substance. (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 1.)

Reply Obj. 1: Augustine means that it is laughable that many souls are asserted to belong to different men only in this sense, that they differ in number and in species, and especially according to the opinion of the Platonists that there is some one general subsisting being above all the things which belong to one species. (Cf. Aristotle, Metaphysics 1.6, 987a29–b18; Aquinas, Commentary on the Metaphysics, bk. 1, lect. 10, n. 153.)

Reply Obj. 2: The angels, just as they possess no matter of which they are made, so they do not possess matter in which they exist; but the soul has matter in which it exists, and consequently the angels cannot be many in one species, but souls can be many of one species.

Reply Obj. 3: As the body is related to the soul’s actual being, so it is to its individuation, because each individual thing is both one and a being on the same basis. A soul’s actual being accrues to it in consequence of its being united to a body with which it simultaneously constitutes one nature, whereof both are a part. And yet, because the intellectual soul is a form that transcends the capacity of the body, it possesses an actual being of its own on a higher level than the body; hence, after the body has been destroyed, the soul’s actual being still remains. Similarly, souls are multiplied along with bodies, and yet when the bodies have been removed, a multiplicity of souls still remains.

Reply Obj. 4: Although the body is not of the essence of the soul, yet the soul because of its own essence has a relation to the body, inasmuch as it is essential for it to be the form of a body. Accordingly, body is set down in the definition of the soul. (Cf. Aristotle, On the Soul 2.1, 412b5.) Just as, accordingly, it is essential to the soul that it be the form of a body, so it is essential to “this soul,” insofar as it is “this soul,” that it have a relation to “this body.”

Reply Obj. 5: Augustine’s statement in that passage is based on the opinion of those who assert that there is one universal soul, as is clear from the preceding context.

Reply Obj. 6: Averroes seems to lay special stress on this argument, (Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 5.) because it would follow, as he himself says, that, if the potential intellect were not one in all men, the thing that is understood would be individuated and counted by means of the individuation and counting of individual men, and thus it would be understood potentially and not in act. It must accordingly be shown that, first, those incongruities follow no less for those who assert that there is one potential intellect than for those who assert that it is multiplied in many. First of all, as regards individuation, it is obvious that a form that exists in some individual is individuated by that individual in the same way, whether it be the only individual in some one species, like the sun, or whether there be many in one species, like pearls. For in both cases the species “brightness” is individuated. One must say that the potential intellect is a kind of singular individual thing, for acts belong to individuals. (See above: a. 5, obj. 8.) Whether, then, it is one in one species or many, the thing that is understood will be individuated in it in the same way. But as regards multiplication, it is obvious that if there are not many potential intellects in the human species, there are, nevertheless, many intellects in the universe, and many of them understand one and the same thing. The same difficulty, therefore, will remain whether the thing that is understood is one or many in different men. Therefore, it is not possible to prove his point by this means, because even after this stand has been taken, the same incongruities will still remain.

Consequently, for the solution of this problem it must be borne in mind that if we have to speak of the intellect by way of a comparison with the senses, as is clear from the procedure of Aristotle in On the Soul 3, (Aristotle, On the Soul 3.4, 429a15–b5; cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 1.) we must say that the thing which is understood is not related to the potential intellect as an intelligible species whereby the potential intellect is actuated, but that species is as a formal principle whereby the intellect understands. Now, that which is understood, or the thing which is understood, is as something which is constituted or formed through the activity of the intellect, whether this thing be a simple quiddity or whether it be the composition and division of a proposition.

Aristotle specifies these two activities of the intellect in On the Soul 3, the one activity, namely, which he calls the understanding of indivisible things, (Aristotle, On the Soul 3.6, 430a26–28; cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 5, n. 746.) whereby the intellect apprehends the essence of a given thing, and this the Arabs call “formation” or “imagination by the intellect,” but he posits another activity, namely, the combining and separating of concepts, which the Arabs call “belief” or “faith.” (Cf. Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 21, 27; see also comm. 26, 33, 36.)

For both of these activities an intelligible species is presupposed, whereby the potential intellect is actuated, because the potential intellect does not act except according as it is in act, just as the sight does not see except through being actuated by a species which makes seeing possible. Hence, the species which makes seeing possible is not as a thing which is seen, but as that whereby the object is seen. The same is true of the potential intellect, except that the potential intellect reflects upon itself and upon its own species, whereas the sight does not.

Accordingly, a thing that is understood by two intellects is in a way one and the same thing, and in a way it is many things, because on the part of the object which is known it is one and the same thing, but on the part of the knowledge itself it is two different things.

Thus, for instance, if two persons should see one wall, it is the same thing which is seen so far as the thing which is seen is concerned, yet it is two different things from the standpoint of the different acts of seeing, and there would be something exactly like this on the part of the intellect, if the thing which is understood subsisted outside the soul as does the thing which is seen, as the Platonists asserted. But according to the view of Aristotle, there seems to be a greater difficulty, although the explanation is the same if one looks into the matter rightly.

For there is no difference between Aristotle and Plato, except in this, that Plato asserted that the thing which is understood has actual being outside the soul in exactly the same way as the intellect understands it, that is, as something abstract and universal, but Aristotle asserted that the thing which is understood is outside the soul, but in another way, because it is understood in the abstract and has actual being in the concrete. Just as, according to Plato, the thing itself which is understood is outside the soul itself, so it is according to Aristotle, and this is clear from the fact that neither of them asserted that the sciences have to do with those things which are in our intellect, as with substances. But whereas Plato said that the sciences have to do with separated forms, Aristotle said that they have to do with the quiddities of things that exist in those things.

Yet the account of universality, which consists in commonness and abstractness, is merely the result of the mode of understanding, inasmuch as we understand things abstractly and universally. But according to Plato, it is also the result of the mode of existence of the abstract forms, and consequently Plato asserted that universals subsist whereas Aristotle did not. (Cf. Aristotle, Metaphysics 1.6, 987b1–14; 7.14, 1039a24–33; Boethius, Commentary on Porphyry’s Isagogue, bk. 2, ch. 11 (PL 64:85A; CSEL 48:167).) Thus, it is clear how the plurality of intellects does not militate against the universality, nor the generality, nor the unity of the thing that is understood.

Reply Obj. 7: Knowledge is caused by a teacher in a pupil, not as heat is caused in faggots by fire, but as health in a sick person by a doctor, who causes health inasmuch as he furnishes some remedies which nature makes use of to cause health, and consequently the doctor proceeds in the same order, in his curing, as nature would cure. For just as the principal healing force is one’s interior nature, so the principle which chiefly causes knowledge is something intrinsic, namely, the light of the agent intellect, whereby knowledge is caused in us, when we descend through the application of universal principles to some special points, which we gain through experience in discovery. Similarly, the teacher draws universal principles down to special conclusions; hence, Aristotle says in Posterior Analytics 1 that a demonstration is a syllogism that causes knowledge. (Aristotle, Posterior Analytics 1.2, 71b17–18; cf. Aquinas, Commentary on the Posterior Analytics, bk. 1, lect. 4.)

Reply Obj. 8: In this reasoning, Averroes also was deceived. For he thought that because Aristotle said that the potential intellect is something separate, it would be separated in existence, and as a consequence would not be multiplied in consequence of the multiplication of bodies. (Cf. Averroes, Commentary on Aristotle’s On the Soul, bk. 3, especially comm. 4.) But Aristotle means that the potential intellect is a power of the soul, which is not an act of any organ, as though it were to have an activity of its own through some corporeal organ, just as the visual power is the power of an organ and has its activity through a corporeal organ. Because the potential intellect does not have its activity through a corporeal organ, it is, consequently, not necessary that it know only those things which have an affinity either with the whole body or with a part of the body. (Cf. Aristotle, On the Soul 3.4, 429a24–27; Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 1.)

Reply Obj. 9: The opinion which holds that the soul is composed of matter and form is entirely false and unprovable. (Above: a. 1, resp.) For it could not be the form of the body if it were composed of matter and form. If the soul were the form of the body in view of its own form only, it would follow that one and the same form would perfect the different kinds of matter of different genera, namely, the spiritual matter of the soul and corporeal matter, and this is impossible since a proper potency has its own proper act. Furthermore, that thing composed of matter and form would not be the soul, but the form of the soul. For whenever we say “soul,” we mean that which is the form of the body. But if the form of the soul were the form of the body through the medium of its own matter, as color is an act of a body through the medium of the surface, so that in this way the whole soul could be called the form of the body—this is impossible, because by “matter” we mean that which is in potency only, but what is in potency only cannot be the act of anything, that is, be a form. But if someone were to mean by the term “matter” a given act, we need not mind, for nothing prevents someone else from calling “matter” what we call “act”; just as, for instance, what we call “stone,” someone else can call “ass.”

Reply Obj. 10: As the Seine river is not “this particular river” because of “this flowing water,” but because of “this source” and “this bed,” and hence is always called the same river, although there may be other water flowing down it, likewise a people is the same, not because of a sameness of soul or of men, but because of the same dwelling place, or rather because of the same laws and the same manner of living, as Aristotle says in Politics 3. (Aristotle, Politics 3.3, 1276a34–b15; cf. Aquinas, Commentary on the Politics, bk. 3, lect. 2.)

Reply Obj. 11: Time is related to one movement only as an accident is to a subject, namely, to the movement of the first movable thing by which all other movements are measured. To other movements time is related as a measure to a thing that is measured; (Cf. Aristotle, Physics 4.12, 220b15–221a6; Aquinas, Commentary on Aristotle’s Physics, bk. 4, lect. 19, n. 598; Averroes, Commentary on Aristotle’s Physics, bk. 4, comm. 101.) so, for instance, an ell is related to a wooden rod as to a subject, but to a piece of cloth which is measured by it as to a thing that is measured only. Consequently, it does not follow that one accident is in many subjects.

Reply Obj. 12: Seeing is not caused by rays that are sent out, as a matter of fact; but Augustine says this according to the opinion of others. (See Augustine, On the Magnitude of the Soul, bk. 1, ch. 23, para. 43 (PL 32:1060; CSEL 89); On the Literal Interpretation of Genesis, bk. 1, ch. 16, para. 31 (PL 34:258; CSEL 28:23), bk. 4, ch. 34, para. 54 (PL 34:319–20; CSEL 28:134–35); On the Trinity, bk. 9, ch. 3, para. 3 (PL 42:962–63; CCSL 50:296).) But supposing this to be true, the soul would quicken rays, however far they are sent out, not as foreign bodies, but insofar as they are connected with its own body.

Reply Obj. 13: As is clear from what has been said above, (Above: ad 6.) a thing that is understood is not individuated nor multiplied except from the standpoint of intellectual activity. It is not incongruous that from a thing that is understood, insofar as it is understood, there is still abstracted a thing that is understood in an absolute sense, just as from “this particular understanding being,” for instance, is abstracted “understanding being” in an absolute sense. Nor does this militate against the account of universality. For it is accidental to man or to the concept “species,” that it is understood by me; hence, it is not essential to the understanding of man or the concept “species” that it be understood by me or by someone else.

Reply Obj. 14: Agreement on first principles is not caused by a oneness of the potential intellect but by that likeness of nature in consequence of which we all are inclined toward the same thing; thus, for instance, all sheep agree in considering a wolf as an enemy, (Cf. Aquinas, Commentary on Aristotle’s Metaphysics, bk. 1, lect. 1, n. 11.) yet no one would say that there is only one soul in them.

Reply Obj. 15: “To be something individual” is not incompatible with “being understood in act,” because separated substances are understood in act although they are, nevertheless, individual substances. Otherwise, they would not have actions, which belong to singular things. (Above: a. 5, obj. 8.) But “to have material being” is incompatible with “being understood in act.” Consequently, individual forms which are individuated by matter are not understood in act, but in potency only. Now, the intellectual soul is not so individuated by matter as to become a material form, especially in view of its intellect, in consequence of which it transcends its relationship to corporeal matter. But in this sense it is individuated on the basis of corporeal matter, as has been said, (Above: ad 4.) namely, inasmuch as it has an aptitude for being the form of “this particular body.” Hence, it is not thereby impossible for the potential intellect of “this particular man” to be understood in act, and the same applies to those things which are received in the intellect.

Reply Obj. 16–17: Through this the solution to the two following arguments is clear.