Article 16 — Whether the soul, when united to the body, can understand separate substances

Sixteenth, it is asked whether the soul, when united to the body, can understand separate substances. (Parallel texts: ST I.88.1; SCG II.6; III.42–44, 46; On Truth, q. 10, a. 2; q. 18, a. 5, ad 7–8; Commentary on Boethius’s De Trinitate, q. 6, a. 3; Commentary on Aristotle’s Metaphysics, bk. 2, lect. 1.)

Obj. 1: It seems that it can. (Cf. Aristotle, On the Soul 3.7, 431b17–19; Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 36; Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 6.) For no form is prevented from attaining its end by the matter to which it is naturally united. (Cf. ST I.88.1, obj. 3; In II Sent., d. 23, q. 2, a. 1, obj. 5.) Now the end of the intellective soul seems to consist in knowing separate substances, which are in the highest degree intelligible. For the end of each and every thing is to attain perfection in its operation. (Cf. Aristotle, Ethics 1.7, 1097b22–1098a10; 10.7, 1177a12; Aquinas, Commentary on Aristotle’s Ethics, bk. 1, lect. 1 and 10.) Therefore, the human soul is not prevented from understanding separate substances by being united to the body, which is the soul’s own proper matter.

Obj. 2: Further, the end of man is happiness. Now according to the Philosopher in Ethics 10, ultimate happiness consists in the operation of man’s highest power, namely, the intellect, and is related to the noblest object, which seems to be none other than a separate substance. (Aristotle, Nicomachean Ethics 10.7, 1177a11–21; 10.8, 1178b10.) Hence, man’s last end consists in understanding separate substances. Now it would be incongruous if man failed completely to attain his end; for in that case his life would be meaningless. Therefore, man can know separate substances. But it belongs to man’s very essence to possess a soul that is united to a body. Therefore, the soul, when it is united to the body, can understand separate substances.

Obj. 3: Further, every generative process reaches a terminus, for no process goes on to infinity. Now there is a certain intellectual generation whereby the intellect is brought from potency to act, that is to say, is made actually knowing. Therefore, this process does not go on to infinity but at some time will reach a terminus, that is, it will be completely actualized. But this end can be attained only when the intellect understands all intelligible things, especially separate substances. Therefore, the human intellect is capable of attaining a knowledge of separate substances. (Cf. Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 36; Aquinas, On Truth, q. 18, a. 4, resp.; SCG III.42.)

Obj. 4: Further, it seems to be more difficult to separate from matter things which do not exist in separation therefrom, and to apprehend those things, than to apprehend things which exist in themselves apart from matter. (Cf. Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 36; Themistius, Commentary on the De anima, bk. 6, ch. 7; Aquinas, On Truth, q. 18, a. 5, obj. 4 and ad 8; SCG III.45.) But even when united to the body, our intellect separates from matter things which do not in themselves exist apart from matter, inasmuch as it abstracts the intelligible species by which it apprehends material things. (Cf. Aristotle, On the Soul 3.5, 430a15.) Therefore, our intellect will be even more capable of apprehending separate substances.

Obj. 5: Further, sensible objects that are excessively intense are sensed to a lesser degree than others, for they destroy the harmony of a sense organ. (Cf. Aristotle, On the Soul 3.4, 429a29–b5; Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 1; On Truth, q. 18, a. 5, obj. 7; ST I.88.1, obj. 3.) However, if there were a sense organ which was not affected adversely by the intensity of its sensible object, then the more intense the sensible object, the more fully would the sense organ experience that object. Now the intellect is not corrupted in any way by an intelligible object, rather is it perfected by it. (Cf. Aristotle, On the Soul 3.4, 429b3–4; 2.5, 417b2–11; Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 3; bk. 2, lect. 11.) Hence, the more intelligible things are, the better the intellect knows them. But separate substances which are actually intelligible in themselves, because they are immaterial, are more intelligible than material substances, which are intelligible only potentially. Therefore, since the intellective soul apprehends material substances when it is united to the body, it is even more capable of apprehending separate substances.

Obj. 6: Further, even when the intellective soul is united to the body, it abstracts the quiddity from things having a quiddity; and, since it cannot regress to infinity, it must in this abstractive process eventually attain to a quiddity that is not a thing having a quiddity but is a quiddity only. (Cf. Aristotle, Posterior Analytics 1.21, 82b38; 1.22, 83b6; Physics 3.4, 204a3–5.) Therefore, since separate substances are nothing but certain quiddities existing of themselves, it seems that the intellective soul, when united to the body, is capable of apprehending separate substances. (Cf. Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 36; On Truth, q. 18, a. 5, obj. 6 and ad 8; SCG III.41.)

Obj. 7: Further, it is natural for us to acquire a knowledge of causes from their effects. However, some of the effects caused by separate substances must be found in sensible and material things; for, as Augustine shows in On the Trinity 3, all corporeal things are governed by God through the agency of the angels. (Augustine, On the Trinity, bk. 3, ch. 4 (CCSL 50:135–37; PL 42:873–74).) Therefore, the soul, when united to the body, can apprehend separate substances through sensible objects.

Obj. 8: Further, the soul understands itself when it is united to the body; for, as Augustine says in On the Trinity 9, the mind understands itself and loves itself. (Augustine, On the Trinity, bk. 9, cc. 3–4 (CCSL 50:295–300; PL 42:962–65).) But the mind itself possesses the nature of a separate intellectual substance. Therefore, the soul, when united to the body, can apprehend separate substances. (Cf. Aquinas, On Truth, q. 18, a. 5, obj. 9; SCG III.46.)

Obj. 9: Further, in things nothing exists without a purpose. (Cf. Aristotle, On the Soul 3.9, 432b21–22; ST I.88.1, obj. 4.) But to be an intelligible seems to be purposeless if the intelligible is not apprehended by any intellect. Therefore, since separate substances are intelligibles, our intellect can apprehend them.

Obj. 10: Further, as sight is to visible things, so intelligence is to intelligible things. But our sense of sight can perceive all visible things, even those that are incorruptible, although it is itself corruptible. (Against Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 36.) Therefore, on the assumption that our intellect is corruptible, it would be capable of apprehending incorruptible separate substances because they are intelligibles in themselves. (Cf. ST I.88.1, obj. 5.)

On the contrary, the soul does not apprehend anything without a phantasm, as the Philosopher says in On the Soul 3. (Aristotle, On the Soul 3.7, 431a16–17.) Therefore, the soul, when united to the body, cannot apprehend separate substances.

I answer that Aristotle set out to solve the problem posed in this article in On the Soul 3, but the solution is not found in those writings of his which have come down to us. (Aristotle, On the Soul 3.7, 431b19; cf. Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 36; Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 6; On Truth, q. 18, a. 5, ad 8; On the Unity of the Intellect, ch. 1.) This explains why Aristotle’s followers have proceeded to offer various solutions for this problem.

For some have maintained that our soul, even when united to the body, is capable of knowing separate substances, and that man’s ultimate happiness actually consists in knowing such substances. (Cf. Aquinas, On Truth, q. 18, a. 5, ad 8; SCG III.41.) However, these theorists entertain different opinions as to the way in which we understand such substances.

For some have maintained that our soul cannot acquire an understanding of separate substances in the way in which we acquire an understanding of those other intelligible objects which we learn about in the speculative sciences. The latter type of knowledge is acquired through definitions and demonstrations, whereas a knowledge of separate substances, these theorists maintained, can be acquired only as a result of the agent intellect itself being united to us. (Cf. ST I.88.1, resp.) For they supposed that the agent intellect was a separate substance which by its own nature understands separate substances. (Cf. Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 17.) Hence, when this agent intellect shall be united to us, enabling us thereby to understand through itself, as we now understand through intellectual habits of scientific knowledge, we shall, consequently, apprehend separate substances.

Moreover, they explain the manner in which this agent intellect can be united to us so that we may understand. For it is evident from what the Philosopher says in On the Soul 2, that whenever we are said to be so-and-so or to do so-and-so, two things are involved, one having the role of form, the other the role of matter; just as we are said to be made healthy by health and with respect to the body, so that health is related to the body as a form to matter. (Aristotle, On the Soul 2.2, 414a4–14.) It is clear also, they say, that we understand by the agent intellect and through intelligible objects-known; for we arrive at a knowledge of conclusions through principles known naturally and through the agent intellect. (Cf. Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 36.) Therefore, the agent intellect must be related to intelligible objects-known as a principal agent is to an instrument, and as a form is to matter, or as act is to potency. (Cf. Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 36; Aquinas, On Truth, q. 18, a. 5, ad 8; SCG III.43; ST I.88.1, resp.) For of two things, the more perfect always has the character of an act with respect to the other.

Moreover, whatever receives in itself that which has the character of a form also receives that which has the character of matter, just as a body having a surface is also receptive of color, which is a kind of form possessed by that surface. Likewise, the pupil of the eye which receives color also receives light, which is the act of color, for by light color is made actually visible. (This is the opinion of Avempace (Ibn Bajja, ca. 1085–1138 AD), according to Averroes and Albert: Averroes, Commentary on Aristotle’s On the Soul, bk. 2, comm. 67; Albert the Great, Summa de homine, tract. 1, q. 21, a. 3, part. 1. And this opinion is contrary to that of Aristotle and Aquinas: Aristotle, On the Soul 2.7, 418a31; Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 14.)

Consequently, in the same way, so far as the potential intellect receives intelligible objects-known, to that extent does it receive from the agent intellect. Hence, when the potential intellect receives all objects-known, then at that time it will receive the agent intellect unto itself completely, and thus the agent intellect will assume the character of a form in the potential intellect, and it consequently will become one with us. (Cf. ST I.88.1, resp.)

Hence, as we at present understand through the potential intellect, so shall we then understand through the agent intellect, and we shall understand not only all natural things but separate substances as well.

On this point, however, there are differences of opinion among those who subscribe to the theory stated above. For some, holding that the potential intellect is corruptible, assert that the potential intellect is in no way able to know either the agent intellect or the separate substances; but that as long as we remain in a state of union with the agent intellect, we shall know the agent intellect and other separate substances as well through the agent intellect itself, inasmuch as it will be united to us as a form. (According to Averroes, Alexander of Aphrodisias, among others, thought that the potential intellect (which Averroes infelicitously calls the “material intellect”) was generable and corruptible. Cf. Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 36. Cf. Aquinas, On Truth, q. 18, a. 5, ad 8; SCG III.42.) But others, holding that the potential intellect is incorruptible, assert that the potential intellect is able to know the agent intellect as well as other separate substances. (This is the opinion of Themistius and Averroes, according to Aquinas: On Truth, q. 18, a. 5.)

Now it is impossible to maintain this position. It is gratuitous and contrary to the meaning of Aristotle’s doctrine. It is impossible to maintain this position because it premises two contradictory affirmations, namely, that the agent intellect is a separate substance existing apart from us, and that we understand through the agent intellect as through a form. Now so far as we carry out an operation by means of something having the character of a form, to that extent do we cause something to exist actually, just as a hot thing heats by its heat inasmuch as it is actually hot. For a thing acts only so far as it is in act. (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 1.) Hence, that by which a thing acts or operates formally must be united to that thing with respect to its very act of existing. (Cf. SCG III.42; ST I.88.1, resp.) Hence, in the case of two substances existing in separation from one another, it is impossible for one of them to operate formally through the other. Thus, if the agent intellect is a separate substance existing apart from us, we cannot understand by it formally, although we may be able to understand by it actively, as we are said to see by the light of the sun.

The aforesaid position is likewise gratuitous because the arguments advanced for it are not conclusive with necessity. Two considerations make this point clear.

The first, indeed, is because if, as the advocates of this view maintain, the agent intellect is a separate substance, then this intellect will not be related to intelligible objects-known as light is to colors, but as the sun shining is to colors. (Cf. Aristotle, On the Soul 3.5, 430a15–16; Avicenna, De anima, part 5, ch. 5.) Hence, simply because the potential intellect receives intelligible objects-known, that intellect is not thereby brought into substantial union with the agent intellect, but is united only to an effect of it, just as the eye by receiving colors is not united to the substance of the sun, but only to the sun’s light. (Cf. ST I.88.1, resp.)

The second is because—supposing we grant that the potential intellect, being receptive of intelligible objects-known, is in some way united substantially to the agent intellect—even though the potential intellect receives all intelligible objects-known, the latter being abstracted from phantasms and known demonstratively through the principles of demonstration, it would not follow that the potential intellect had thus been perfectly united with the agent intellect. This could be the case only if it were proved that all those intelligible objects together were equivalent in power and in substance to the power and substance of the agent intellect itself. (Cf. ST III.43; I.88.1.) This is obviously untrue, for if the agent intellect is a separate substance, it is by that fact alone of a higher order of being than all those objects in the natural order which are rendered intelligible by it.

It is also remarkable that these people did not see the evident error in their reasoning. For, although they maintained that all intelligible objects-known were united by one or two of these objects, still it does not follow for this reason, according to them, that we shall know all the other intelligible objects-known. Now it is evident that separate intelligible substances surpass all those objects which they call intelligible objects-known to a far greater degree than all of the latter taken together exceed one or two or any number of themselves. For these objects are all of one genus and have the same mode of intelligibility, whereas separate substances are of a higher order, and have a higher mode of intelligibility. (Cf. Aquinas, On Truth, q. 18, a. 5, resp.; SCG III.43.) Hence, if the agent intellect is brought into union with us as a form and as the agent of those intelligibles, it does not for this reason follow that it is united to us as a knower of separate substances.

It is likewise clear that this whole position is contrary to the intention of Aristotle, who says in Ethics 1 that happiness is a common good which all who are not deprived of virtue may possess. (Aristotle, Nicomachean Ethics 1.9, 1099b18–20; cf. Aquinas, Commentary on Aristotle’s Ethics, bk. 1, lect. 14; SCG III.44; ST I.88.5.) But to understand all those things which these theorists call intelligible objects-known is impossible for any man, (Cf. SCG III.44.) or at least so rare that in this life no man ever did in fact attain such understanding, except Christ himself, who was both God and man. (Cf. Aquinas, On Truth, q. 10, a. 11, ad 3; q. 18, a. 4, resp. and ad 10.) Hence, it is impossible that such knowledge should be required for human happiness. Now the ultimate happiness of man consists in knowing the noblest intelligible objects, as the Philosopher says in Ethics 10. (Aristotle, Nicomachean Ethics 10.7, 1177a12–21; 10.8, 1179a23–32; cf. Aquinas, Commentary on Aristotle’s Ethics, bk. 10, lect. 10; SCG III.44; ST I.88.1, resp.) Thus, it is not necessary for a man to know all intelligible objects-known in order to know those substances which are the noblest intelligibles, and in the knowledge of which human happiness consists.

In another way this whole position is evidently contrary to the meaning of Aristotle’s doctrine. For it is said in Ethics 1 that happiness consists in acting in accordance with perfect virtue. (Aristotle, Nicomachean Ethics 1.7, 1098a15–17; 1.13, 1102a5.) So in order to show clearly and precisely what happiness actually consists in, Aristotle found it necessary, as he says near the end of Ethics 1, to determine the nature of all the virtues. (Aristotle, Nicomachean Ethics 1.13, 1102a5, 1103a3–10.) He maintains that some of these are moral virtues, such as fortitude, temperance, and the like; however, others are intellectual virtues, which he held to be five in number: wisdom, understanding, science, prudence, and art. He says that the chief of these is wisdom, and that ultimate happiness consists in the exercise of wisdom, as appears in his text. (Aristotle, Nicomachean Ethics 10.8, 1179a22–32; cf. Aquinas, Commentary on Aristotle’s Ethics, bk. 10, lect. 13.) Moreover, it is clear from the beginning of Metaphysics that wisdom is first philosophy itself. (Aristotle, Metaphysics 1.2, 982b7–10.) Hence, it follows, according to Aristotle, that the ultimate human happiness which can be had in this life consists in such knowledge of separate substances as can be acquired through the principles of philosophy, and not through any union with an agent intellect, such as some have vainly imagined.

Wherefore, there is another theory according to which the human soul can attain to an understanding of separate substances through the principles of philosophy. (According to Averroes, this is the opinion of Avempace: Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 36; cf. SCG III.41; ST I.88.2.) The upholders of this theory proceeded to demonstrate their position as follows. It is evident that the human soul can abstract quiddities from material things and can apprehend them; for this is precisely what happens whenever we grasp what a material thing is. Now if that abstracted quiddity is not a pure quiddity but is itself a thing having a quiddity, then even so the intellect must eventually succeed in grasping the simple quiddity itself alone because it is impossible to go on to infinity in the process of abstraction. And by contemplating simple quiddities, our intellect is, in fact, understanding separate substances because the latter are themselves nothing else than simple quiddities.

However, this argument is entirely inadequate: first of all because the quiddities of material things are of a different order from separate quiddities and have a different mode of existing; so it does not follow that our intellect understands separate quiddities simply because it grasps the quiddities of material things. (Cf. Aquinas, Commentary on Boethius’s De Trinitate, q. 6, aa. 3–4, resp.; On Truth, q. 10, a. 11, resp.; SCG III.41; ST I.88.2, ad 4.) In the second place, the diverse quiddities apprehended by the intellect themselves differ in species, so that a person who apprehends the quiddity of one material thing does not thereby apprehend the quiddity of another; for example, to understand what is a “stone” is not to understand what “animal” is. Thus, even if we granted that separate quiddities are of the same account as material quiddities, it would follow that one who understands the latter likewise understands the former, unless one happened to subscribe to Plato’s view that separate substances are the species of these sensible things. (Aristotle, Metaphysics 1.6, 987b1–14; cf. SCG II.92.)

Consequently, in opposition to this doctrine, we must maintain that the intellectual soul of man, by being united to the body, has its vision turned toward phantasms, and is informed in its understanding only through species acquired from phantasms. (Cf. SCG III.45; ST I.88.1.) This agrees with the statement of Dionysius in chapter 1 of The Celestial Hierarchy, for he says, the divine light can shine upon us only when screened round about by many sacred veils. (Pseudo-Dionysius, The Celestial Hierarchy, ch. 1, para. 2 (PG 3:121–22); cf. Aquinas, On Truth, q. 18, a. 5, resp.; Commentary on Boethius’s De Trinitate, q. 6, a. 3, resp.) Hence, the soul, while united to the body, is capable of attaining a knowledge of separate substances only so far as it can be led thereto through species derived from phantasms. But in this way the soul will not attain quidditative knowledge of those substances, because their order of intelligibility transcends completely that of the intelligible species of material things abstracted from phantasms.

However, we can in this way attain some knowledge of those separate substances: we can know that they exist, just as from lowly and deficient effects we proceed to lofty causes, but only to the extent that we know they exist. And while we know that these superior causes exist, at the same time we know that they are not of the same nature as their effects, and this knowledge consists in knowing what they are not, rather than what they are. Consequently, it is true to say that, inasmuch as we grasp the quiddities which we abstract from material things, our intellect can, by turning to those quiddities, apprehend separate substances, so that it knows them to be immaterial, just as are the quiddities themselves which are abstracted from matter. Thus, thanks to the reflective power of our intellect, we are brought to a knowledge of intelligible separate substances. Nor is there cause for wonder if in this life we are incapable of knowing separate substances in their very essence, but we can know only what they are not. (Aquinas defines the limits of human knowledge in On Being and Essence, ch. 5.) For it is only in this way that we can know even the quiddity and nature of the heavenly bodies. Thus, in On the Heavens 1, Aristotle shows that the heavenly bodies are neither heavy nor light, generable nor corruptible, nor subject to contrariety. (Aristotle, On the Heavens 1.10, 279b5; 1.3, 269b26–30; 270a12–22; cf. ST I.88.2, ad 2.)

Reply Obj. 1: The end to which the natural power of the human soul is directed is to know separate substances in the manner explained above, (Above: resp.) and the soul is not prevented from attaining this end because of its union with the body. Nor does the ultimate happiness of man, so far as it can be attained by his natural powers, consists in such knowledge.

Reply Obj. 2: Thus, the answer to the second objection is evident.

Reply Obj. 3: Although the potential intellect is continually being brought from potency to act by understanding more and more, nevertheless this reduction or generation will find its term in understanding the supremely intelligible object, namely, the divine essence. But the intellect cannot attain to this understanding by its natural powers, but only by grace. (Cf. Aquinas, On Truth, q. 10, a. 11, resp., ad 7.)

Reply Obj. 4: It is more difficult to separate and to understand things which are not separate than it is to understand things which are separate, if it is a question of the same things. But in the case of different things, this is not necessarily so; for more difficulty may be experienced merely in understanding one separate thing than in abstracting and understanding others. (Cf. Aquinas, On Truth, q. 18, a. 5, ad 4.)

Reply Obj. 5: With respect to sensible objects of excessive intensity, a sensory power is subject to a twofold deficiency: one, in that such objects exceed the grasp of sense since they are out of proportion to its powers; (Cf. Aristotle, On the Soul 2.12, 424a28–31; 3.4, 429a29–b5; Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 24 and 26; bk. 3, lect. 1.) another, in that, after the impact of such objects on the sense, the sense is incapable of perceiving sensible objects that are not as intense, because the sense organ has already been made inoperative. Therefore, although the intellect does not have an organ which can be made inoperative by an intelligible object of great intensity, yet something supremely intelligible can exceed the intellective power of our intelligence. Such an object is a separate substance, which exceeds the power of our intelligence, for our intelligence, inasmuch as it is united to the body, is naturally disposed to be actuated and perfected by species abstracted from phantasms. Nevertheless, if our intelligence did apprehend separate substances, it would have not less but greater understanding of other things. (Cf. Aquinas, On Truth, q. 18, a. 5, ad 7.)

Reply Obj. 6: As was shown, the quiddities abstracted from material things do not suffice as means through which we can acquire quidditative knowledge of separate substances. (Cf. Aquinas, On Truth, q. 18, a. 5, ad 6; SCG III.41.)

Reply Obj. 7: The same answer applies to the seventh objection; for, as we have said above, effects that do not adequately reflect their causes do not suffice as means through which their causes can be known quidditatively.

Reply Obj. 8: Our potential intellect does not know itself directly by apprehending its own essence, but through a species abstracted from phantasms. For this reason, the Philosopher says in On the Soul 3 that the potential intellect is itself intelligible like other things. (Aristotle, On the Soul 3.4, 429b9; 430a2–3; cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 3; SCG II.98; III.46.) The reason for this is that nothing is intelligible so far as it is in potency, but only so far as it is in act, as is said in Metaphysics 9. (Aristotle, Metaphysics 9.9, 1051a29–33.) Hence, since the potential intellect is only in potency with respect to intelligible being, it can be known only through the form by which it is actuated, namely, by a species abstracted from phantasms, just as everything else is known through the form which it has. That acts are known through objects, powers through acts, and the soul through its powers, is indeed common to all the powers of the soul. (Cf. Aristotle, On the Soul 1.1, 403a10–12.) So likewise the intellective soul is known through its own act of understanding. However, a species abstracted from phantasms is not the form of a separate substance through which that substance can be known in the same way as the potential intellect is understood through that form.

Reply Obj. 9: (Cf. ST I.88.1, ad 4.) This argument is entirely ineffective for two reasons: first, because intelligibles do not exist in order that intellects may know them; they rather exist as the ends and perfections of intellects. Consequently, if an intelligible substance existed which was not actually known by any intellect other than itself, this substance would not for that reason exist in vain. For the expression “in vain” is said of that which concerns the end that a thing fails to reach. Second, the argument of this objection is ineffective because, even if separate substances are not apprehended by our intellect while united to the body, yet they are apprehended by separate substances. (Cf. SCG III.45.)

Reply Obj. 10: (Cf. ST I.88.1, ad 5.) The species of which the power of sight is receptive can be the likenesses of any sort of body, whether corruptible or incorruptible. But species abstracted from phantasms, of which the potential intellect is receptive, are not likenesses of separate substances. Hence, there is no ground for a comparison between these two cases.