Sense Cognition: Aristotle vs. Aquinas

by Mortimer J. Adler

Appeared in The New Scholasticism 42 (Autumn 1968): 578-591.

     It is seldom that an author learns anything from a review or discussion of his book. I am most grateful to John Deely for providing an exception to this rule. I learned three important things from his discussion of The Difference of Man and the Difference It Makes, which appeared in the Spring, 1968, issue of The New Scholasticism (Vol. XLII, pp. 293-306).

      (1) I learned that I had made a logical mistake in rejecting the argument for the incorporeality of the intellect based on the simultaneous presence of contraries in a single act of the understanding (see Deely, p. 305, fn. 41).

      (2) I learned that I had overlooked, either from ignorance or inadvertence, a crucial text in Aquinas (much commented on by such contemporary Thomists as Jacques Maritain and Yves Simon) which asserts the immateriality of the quo in sense cognition as well as the immateriality of the quo in intellectual cognition, and which indicates also that the immateriality involved in sense cognition cannot be the same as the immateriality involved in intellectual cognition (see Deely, pp. 297-303). As Mr. Deely generously pointed out, this failure of scholarship on my part did not in any way affect my re-statement of the Thomistic argument in The Difference of Man and the Difference It Makes (henceforth cited as DOM); for I was there concerned only to re-state the argument for the incorporeality of the intellect or power of conceptual thought; i.e., the argument which explains why the quo involved in intellectual cognition cannot be the act of a corporeal organ (see DOM, pp. 220-222 and n. 41, pp. 340-347'). Nevertheless, Mr. Deely is correct in saying that I not only overlooked the crucial text mentioned above, but that I also denied what the text explicitly asserts; for, while affirming that sense cognition and intellectual cognition are both knowledge -- in an analogical not a univocal sense, of that term -- I denied the immateriality of the quo that is involved in sense cognition (see DOM, pp. 214-216; 344).

      (3) This leads me to the third and most important thing that I learned as a result of Mr. Deely's discussion. However, in this case, what I learned came from re-examining certain critical passages in my own book and by coming to understand, better than when I wrote them, why I denied -- and would still deny -- the immateriality of the quo of sense cognition. I have been helped to attain this improved understanding by an exchange of letters with Mr. Deely. The more I have come to understand Mr. Deely's position, in the light of the elucidations of it that he has so patiently elaborated for me, the better I have come to understand my reasons for rejecting it and for re-affirming the position I took in The Difference of Man.

      Mr. Deely would be the first to say that the position that I refer to as his is not his but that of Aquinas, or at least that of Aquinas as interpreted by Cajetan and John of St. Thomas and, in our own day, by Maritain and Simon. I will, therefore, refer to it as the Thomistic position. As for my own position, I would also like to claim that it is not my own, but that of Aristotle, or at least that of Aristotle as I and perhaps others interpret De Anima. I will, therefore, refer to it as the Aristotelian position. Whether Aristotle himself or Aquinas himself actually held the positions here called Thomistic and Aristotelian, we shall never know; and it makes no difference, for what we are here concerned with is an opposition between two philosophical theories, both of which cannot be right but both of which may be wrong.

      I propose to proceed as follows: (I) I will first try to explain why I think the Thomistic position is either self-contradictory or untenable; (II) I will then try to elucidate the Aristotelian position and defend its tenability; (III) since it is possible that both positions are untenable, I will examine some alternatives and consider their tenability; and I will then conclude with an assessment of the Thomistic and the Aristotelian positions by comparing their ability to explain the existence of knowledge while still preserving the mystery of it.


      The Aristotelian and the Thomistic positions agree on a number of points with regard to the process of knowing:

(a) that, in the case of material composites, the form of that which is knowable and can become actually known (i.e., the form of the quod) must be received in the knower, separated from or without its matter (i.e., the matter to which it is united in the quod);

(b) that the knower is potentially a knower by having the power to receive forms in this way, and becomes actually a knower when its cognitive power is actualized by their reception;

(c) that the received form which actualizes a cognitive power is the quo or that whereby the knower actually knows the knowable and makes it actually known;

(d) that the sensible forms of the material composite to be known are received in a cognitive power that is corporeal, whereas the intelligible forms of the material composite to be known are received in a cognitive power that is incorporeal, and

(e) that this radical difference between the phantasm as the quo of sense cognition and the concept as the quo of intellectual cognition explains why the phantasm is the indispensable means of our knowing singulars and the concept is the indispensable means of our knowing universals.

      Without abrogating this radical difference between the phantasm and the concept -- without which the difference between sense cognition and intellectual cognition cannot be understood -- the Thomistic position then departs from the Aristotelian position by asserting that the phantasm, as the quo of sense cognition, must be immaterial in a sense that is at least analogical with the sense in which the concept, as the quo of intellectual cognition, is immaterial. The analogy involves a distinction between two grades of immateriality: one in which the quo is still subject to the individuating conditions derived from matter -- this is the immateriality of the phantasm; the other in which the quo is exempt from such individuating conditions -- this is the immateriality of the concept. This difference between them stems from the fact that the phantasm is an act of the brain, a corporeal organ having cognitive power, whereas the concept is an act of the intellect, an incorporeal cognitive power.

      On the face of it, the Thomistic position appears to be self-contradictory, for it seems to assert that that which exists as the act of a bodily organ also exists immaterially. The grade of immateriality attributed to the phantasm appears to be a mixture of incompatibles -- on the one hand, an immateriality akin to the immateriality of the concept; on the other hand a materiality from which the concept is exempt, namely, the individuating conditions that give the phantasm the singularity that it requires to be the means of our knowing singulars.

      The defender of the Thomistic position will claim that the contradiction is only apparent, not real, and that it is removed by distinguishing between the entitative being of the phantasm as an act of the brain (in which mode of being, it is material) and the intentional being of the phantasm as the quo of sense cognition (in which mode of being it is immaterial). In its entitative being, the phantasm is an act of the knowing subject, like any other act, it is entitatively an accident inherent in that subject; its mode of being is material because it is the act of a cognitive power that is corporeal; the phantasm, in short, exists in the brain of the knowing subject.1 But in its intentional being as the quo of sense cognition, the phantasm does not exist as an accident of the knowing subject; it exists as a relation between the knower and the known -- the relation that constitutes actual knowledge, whereby the potential knower comes actually to know and the knowable comes actually to be known. Through this relation, the subject having the power to know becomes the other -- the subject capable of being known. Whereas the phantasm as an entitative being exists in the knowing subject, and whereas sensible forms exist in the subject to be known, the phantasm as an intentional being does not exist in any subject, but as a relation between subjects. It is for this reason that Mr. Deely identifies intentional being with inter-subjective being and it is this that leads him to relate Heidegger's ontology of the inter-subjective with the Thomistic theory of intentional being.

      Since making distinctions serves to resolve apparent contradictions, it would appear that the distinction between the entitative and intentional being of the phantasm succeeds in removing the contradiction involved in saying that the phantasm is both the act of a corporeal organ and also immaterial, for it is material only in its entitative being as the act of a corporeal organ but not in its intentional being as the relation whereby the knower actually knows and the knowable is actually known. However, this way of removing the contradiction may go too far, for by sharply separating the intentional from the entitative being of the phantasm it generates a puzzle about the materiality that still clings to the phantasm in its intentional being, for in that mode of being it must still be subject to the individuating conditions derived from matter in order to serve as the quo in our knowledge of singulars. Waiving that difficulty, or conceding that it is surmountable, I would now like to state my grounds for thinking that when the Thomistic position is defended in this way against the charge that it is self-contradictory, it is untenable.

      That which is a non-entity is non-existent. Relations do not exist as such; they do not constitute a mode of bring; when two entities are related -- whether they are related as knower and known, as father and son, as double and half, or any other way -- the relation exists entitatively as an accident in each of the relata. It does not exist as something in between them, not inhering in either of them. There is, in short, no inter-subjective mode of being; for everything that exists exists either as a subject (i.e., a substance) or in a subject (i.e., an accident).

      This amounts to saying that if intentional being must be identified with inter-subjective being in order to distinguish intentional from entitative being, then there are no intentional beings -- no existent nonentities. If I am correct in this, then the phantasm does not have an intentional mode of being in addition to and distinct from an entitative mode of being, but only the latter; and in its entitative mode of being, it is the act of a corporeal organ, and so cannot have an immaterial mode of existence in any sense which is either univocal or analogical with the sense in which the concept -- the act of an incorporeal power -- has an immaterial mode of existence.

      The defender of the Thomistic position will now reply by saying that, with the rejection of intentional being, I have made it impossible to explain knowledge. I must call his attention at once to the fact that I have not repudiated any of the five points with which this section began -- five points that are common to the Aristotelian and Thomistic accounts of the process of knowing. Furthermore, in regarding the phantasm or the concept as a quo of knowing, I have retained the notion of intentionality, but denied that intentionality is a special mode of being.2 In the spirit of Ockham's razor, I am charging the Thomist with a needless multiplication of modes of being. The distinction between entitative and intentional being need not be posited to explain knowledge; and since the only justification for positing it would lie in its indispensability for explanatory purposes, we are without grounds for making a distinction that violates the axiom that everything that exists as a subject or in a subject.


      In the course of the foregoing, I have indicated the core of the Aristotelian position. To attribute to the phantasm the intentionality requisite for it to be the quo of sense cognition does not involve attributing to it any mode of existence other than the one it has as an accident of the knowing subject and as an act of a cognitive power -- in this case, a cognitive power vested in a corporeal organ, the brain. Like the phantasm, the concept has no mode of existence other than its entitative existence as an accident of the knowing subject; but unlike the phantasm, the concept exists as the act of a cognitive power that is not vested in a corporeal organ; and so the entitative existence of the concept is immaterial, whereas the entitative existence of the phantasm is material. What gives the phantasm its intentionality -- its ability to function as a quo in the process of knowing -- is identical with what gives the concept its intentionality: they have intentionality because they are the acts of cognitive powers. No other entities (i.e., no accidents other than those that are acts of cognitive powers) have intentionality. The fact that the phantasm exists materially as an act of the brain's cognitive power whereas the concept exists immaterially as an act of the intellect's cognitive power does not affect the intentionality they possess or make it analogical rather than univocal. It is univocal in the sense that whatever is the act of a cognitive power has intentionality. The difference between a corporeal and an incorporeal cognitive power manifests itself only in the difference between singular and universal intentions, not a difference in intentionality as such.3

      The following observations must be added to complete the explication of the Aristotelian position. In both sense cognition and intellectual cognition, the form -- sensible or intelligible -- of the material composite that is the quod of knowledge must be received by the knower separate from the matter with which it is united in the material composite. Otherwise, knowing would be identical with eating. In this sense and only in this sense is the received form immaterial, namely that it is without the matter to which it is united in the quod; it is only in this sense of immateriality that immateriality is always a property of the quo involved in knowing. Furthermore, immateriality in this limited sense is univocally common to the phantasm and the concept. But the phantasm, immaterial in this sense because as a quo it is a sensible form separated from the matter with which it is united in the quod, exists as a quo in another kind of matter -- a kind of matter that is invested with cognitive power and so can be called "cognoscitive matter." Consequently, while immaterial in the sense of being separated from what we may call its "natural matter," it is material in the sense of existing in another kind of matter -- cognoscitive matter. It is this materiality that distinguishes the phantasm from the concept, which is not only immaterial in the sense of being a form that is separated from its natural matter but also immaterial in the sense of existing in no matter at all when it exists as an act of the intellect, an incorporeal power.

      Considered with respect to their mode of being, the phantasm is wholly material and the concept is wholly immaterial. Considered in relation to the natural existence of the sensible or intelligible form, both are immaterial in the very special sense in which the quo of knowing is always a form separated from the natural matter with which it is associated in the material composite that is the quod of our knowing. Let us call the contrasting materiality of the phantasm and immateriality of the concept their existential or entitative materiality and immateriality; and let us call the sense of immateriality that is common to the phantasm and the concept (i.e., the separation of a form from its natural matter) their cognitive or intentional immateriality. The combination of (i) entitative materiality and (ii) intentional immateriality in the phantasm when compared with the combination of (i) entitative immateriality and (ii) intentional immateriality in the concept does not warrant the Thomistic notion of two grades of analogical immateriality, one belonging to the phantasm, the other to the concept. On the contrary, once the senses of materiality and immateriality are carefully distinguished, equivocation lurks in the wings when it is said that not only is the concept immaterial (without adding "in both the intentional and the entitative sense"), but so also is the phantasm immaterial (without adding "in the intentional but not the entitative sense").

      In trying to explain sense cognition, Aristotle employs the example of the impression made by the signet on the wax.4 The letter A embossed on the gold signet, when received in the wax, is separated from the matter of the signet. The golden A on the signet is formally the same as the waxen A, but materially different. Here the wax has the potentiality of receiving the form A without also receiving the matter of the signet; but the form A as received in the matter of the wax can hardly be called immaterial because it is separated from the matter of the signet. When Aristotle says that that which is sensitive "has the power of receiving the sensible forms of things without the matter," the same formulation applies: when the sensible forms of things are received in the sense organ, i.e., the brain,5 they are received without the matter of things whose sensible forms they are; but as received by the matter of the brain they are not forms that are, absolutely speaking separated from matter, but forms that are, relatively speaking, in a different matter.

      One question remains: if the parallelism between sense organ and wax is perfect, why is not the form A as received in the wax a quo that enables the wax to perceive the form embossed on the gold signet? This question goes to the heart of the matter, for it asks how such natural alterations as the heating of the water in a kettle by a hot plate differ from the special kind of change that is an act of sense cognition. In both cases -- in the natural alteration and in the act of sense cognition -- the form of one material thing has passed into another material thing without its matter (i.e., the matter of the first material thing). The answer must lie in the difference between sensitive matter (i.e., matter in which the cognitive power of sense is vested) and all other matter.6

      The wax as matter is like the gold as matter -- non-cognoscitive; both differ from the matter of the brain, which is cognoscitive. Hence when the form A is received in the wax without the gold of the signet, it is just a waxen A instead of a golden A; but when the form A -- or red or hot -- is received in the brain without the matter of the sensible things that are shaped A or are red or hot, the brain does not become red or hot or have impressed on it the shape A. Through the power of the cognoscitive matter in which it is received, the form in question has become the quo of sense cognition -- that whereby the living organism endowed with sensitive matter senses or perceives.7 Instead of becoming other, as does the flat surface of the wax when it is impressed by the A of the gold signet or the cold water in the kettle when it is heated by the hot plate, the living organism becomes the other. This is just another way of saying that a sensible form received in cognoscitive matter results in a cognitive act (i.e., a quo), not a natural alteration.8 A form that is the act of a corporeal cognitive power has intentionality just as much as a form that is the act of an incorporeal cognitive power, though the quo of sense cognition is entitatively material (and hence is the quo involved in our knowing singulars) whereas the quo of intellectual cognition is entitatively immaterial (and hence is the quo involved in our knowing universals).


      Let me suppose for the moment that defenders of the Thomistic position would regard the Aristotelian position that I have just expounded to be as untenable as I have already indicated that I regard the Thomistic position summarized in Section I above. Since these two positions are incompatible, both cannot be true, but it is certainly entertainable that both are false or at least unsatisfactory. Assuming that both are, what alternatives remain? I would like to mention three, though this hardly exhausts the range of theoretical possibilities.

      One alternative consists in denying that there is any such thing as sense cognition by itself, thus reserving intentionality for a quo that is entitatively immaterial -- the quo of intellectual cognition. This would, of course, require us to deny that animals have knowledge; but since we do not know that animals know -- as, reflexively, we know that we ourselves know -- this denial does not come into conflict with any incontrovertible fact of animal behavior.9 However, we do know, again reflexively, that we know singulars, by means of our sensitive powers; and so we are not relieved of the necessity of explaining human sense cognition, even if we were to deny animal sense cognition. But unlike animal sense cognition, human sense cognition is never sense cognition as such, i.e., sense cognition simpliciter or without the simultaneous conjunction of intellectual cognition. It is sense cognition eminenter, or sense cognition transformed by its conjunction or cooperation with intellectual cognition; and so the power of the agent intellect might explain sense cognition eminenter as well as intellectual cognition.10 While this hypothesis is not absolutely impossible, it is beset by difficulties that tend to make it less satisfactory in my judgment than the Aristotelian theory it is offered to replace. I must add, however, that in my judgment it is no more unsatisfactory -- no more beset by difficulties -- than the Thomistic theory it is offered to replace. I would not be able to choose between them.

      A second alternative is the position of Brentano and of the phenomenologists and existentialists who have adopted his theory of intentionality. According to this theory, a non-physical or immaterial mode of being must be posited in order to provide a home for intentionality. That which is entitatively physical or material cannot have intentionality or cannot be an intention. Intentions are mental; intentionality belongs to mental acts. The world is divided into two realms -- the mental realm of intentions, meanings, or consciousness, and the physical realm of the meaningless and unconscious.11 Since Brentano and his followers attribute intentionality to appetitive as well as cognitive acts and, among cognitive act , to perceptual, imaginative, and mnemonic acts as well as to conceptual ratiocinative acts, the world of animal life includes, for them, a mental realm as much as does the world of human life. Though the last thing that phenomenologists and existentialists have any interest in is animal behavior and consciousness, they would be compelled, by the logic of their Brentano premises, to attribute consciousness to animals as well as to men, and they would further be compelled to make that attribution univocal.

      A third alternative is the position taken by a large number of contemporary philosophers who espouse the identity hypothesis as the most satisfactory solution of the mind-body problem. They are materialists, but they are also non-reductionists. The identity hypothesis, as they expound it, holds that brain acts or processes adequately explain or are the sufficient condition of both sense and intellectual cognition. This is what they mean by the identity of mental states (i.e., cognitive acts) with physical states (i.e., brain processes) -- an existential inseparability that allows for (in fact, asserts) the irreducibility of mental states to brain processes.12 Paradoxical though it may seem, the identity hypothesis, therefore, resembles the position of Brentano in three important respects: (i) both posit a mental as well as a physical realm; (ii) for both, the world of animal life includes a mental realm as much as does the world of human life; hence (iii) for both, the difference between men and animals is either one of degree or at most a superficial difference in kind. In contrast, both the Thomistic and the Aristotelian positions, as well as the hypothesis that denies sense cognition in animals, support the view that animals and men differ radically in kind because animals lack what men possess -- an incorporeal power (the intellect) without which human knowledge, specifically our knowledge of universals, cannot be explained.

      As I have tried to make clear in The Difference of Man, the success or failure of future Turing machines in the conversational test will either decisively falsify the proposition that there is a radical difference in kind between men and animals or will greatly increase the probability that that proposition is true.13 In the meantime, Aristotelians and Thomists can hold on to their conviction that they have good reasons for thinking that men differ radically from brutes by virtue of the incorporeal power that must be posited to explain intellectual cognition and even sense cognition eminenter. Though the action of the brain is the sufficient condition of perceptual thought, it is only a necessary, not the sufficient condition, of conceptual thought, without which there is no understanding of universals and without which all percepts are blind.

      This being so, we are left for the time being with a final question about the Aristotelian vs. the Thomistic position. Even though both may have difficulties, as all theories about difficult matters do, which has fewer, or less insurmountable, difficulties and is, therefore more tenable -- more satisfactory?

      The criterion in terms of which I would answer this question is as follows. Of two competing theories, the one which posits less while still explaining all the facts to be explained is the more satisfactory, for it posits only the minimum that is necessary for explanatory purposes while the other theory posits more than is necessary.

      By this criterion, I hold the Aristotelian theory to be more satisfactory than the Thomistic theory. It does not posit a mode of being that is distinct from entitative being; it does not posit an intentional mode of being which, being inter-subjective, consists of beings that are neither subjects nor in subjects.

      The defender of the Thomistic position will counter by saying that though the Aristotelian position may explain the existence of knowledge, it fails to preserve the "mystery" of knowledge, which can be preserved only by positing an intentional mode of being distinct from entitative being. I take it that what is meant by "mystery" -- if it is taken in a philosophical and not a theological sense -- is that which inexorably eludes our power to explain even after we have given the best explanation that we are able to construct. Stated another way, a philosophical mystery is indicated at that point in our explanatory efforts where we can only appeal to the special intervention of divine causality or where we stop trying to explain and say "How this came to be or how it works, God only knows."

      The Thomistic theory preserves the mystery of knowledge at the point at which the theory must appeal to divine causality order to explain the coming to be of intentional beings, since their coming to be cannot be explained by action of purely natural causes.14 In addition, of course, the existence and action in man of the agent intellect cannot be fully explained on the plane of natural causes; but that is a point of mystery which the Thomistic and the Aristotelian theory share. For the Aristotelian theory, the mystery of sense cognition lies in the existence of cognoscitive matter, which, without appealing to God's creative power, we can not fully explain in terms of natural causes any more than we can fully explain the agent intellect.15 Only God knows how they both came to be and how they work.

      The Aristotelian theory preserves the mystery of knowledge as well as the Thomistic theory, it explains the existence of knowledge as well as the Thomistic theory; and it posits less. Therefore, it is the more satisfactory.

Institute for Philosophical Research,
Chicago, Illinois.


      1 See DOM, p. 344; and cf. Aquinas, Summa Theol., I, 76, 1, where it is said that phantasms are not only "in the possible intellect" but also "in corporeal organs."

      2 I am delighted to find that, with one exception, the passages in DOM in which intentionality, meaning, and formal signs are discussed (pp. 214- ; 216, 220, 327-333) do not refer to the quo as an intentional being, but only as being an intention or as having an intentionality. The one exception is on p. 343.

      3 In DOM, p. 216, I remarked that Aristotle and Aquinas regarded "the intentionality of perceptual acts and the intentionality of conceptual acts as analogical, not univocal." They may so regard it, or at least the Thomistic position may; but in my present understanding of the Aristotelian position, the intentionality of the quo of sense cognition and the intentionality of the quo of intellectual cognition are univocal, not analogical. This does not preclude the Aristotelian from holding that animal sense cognition and human sense cognition are both knowledge only in a thinly analogical sense (see fn. 9 below). As for sense cognition (sense cognition eminenter) and intellectual cognition in man, there seems to be no reason for not regarding them as knowledge in a univocal sense of that term.

      4 See De Anima, II, 12, 424a17-24. Cf. ibid., II, 5 and III, 2, 425b27-426a26.

      5 When after saying that "by a 'sense' is meant what has the power of receiving into itself the sensible forms of things without the matter," Aristotle says that "by 'an organ of sense' is meant that in which ultimately such a power is seated," he appears to have in mind such things as the eye, the ear, the nose, the skin, etc. But these are not the organs of sense, for the cognitive power is not ultimately vested in them, but in the brain. Aristotle was simply ignorant of the neurophysiology of sense-perception. Not the eye, but brain-cum retina-cum optic nerve is the organ of vision, as brain-cum cochlea-cum auditory nerve is the organ of hearing and so on for each of the special senses. The so-called "sense organs" are nothing but the afferent appendages of the brain; the brain together with its various afferent inlets is the only sensorium or organ ultimately vested with the power of sense cognition.

      6 See Bernard Lonergan, Verbum (Notre Dame, 1967), pp. 147-161. Unfortunately, in these pages, especially p. 151, Lonergan speaks of the natural and intentional existence of forms instead of saying that a form that exists in its natural matter lacks intentionality, whereas a form that is separated from its natural matter and comes to exist in matter has intentionality.

      7 By behavioristic criteria, which are the only criteria we can employ, we now have machines, e.g., the Perceptron, that can "cognize" shapes and discriminate between different shapes in a manner that is indistinguishable from animal cognition and discrimination. Machines do not yet exist with the power to discriminate between qualities (colors, let us say) as well as shapes; but there is no reason to suppose that a machine cannot be built that will be able to do this as well as a rat. If it occurs, man will have constructed an electronic nerve net or an electro-chemical apparatus that functions in the same way as the nervous system of an animal; he will have produced cognoscitive matter, or a very close simulacrum of it. In that event, the Cartesian view of animals as automata will have been confirmed.

      8 I have long puzzled about the distinction that Aquinas makes between the natural and spiritual immutation of the sense organs. See Summa Theol., I, 78, 3. I think that I can now understand it by identifying it with the distinction between a natural alteration and a cognitive act. Let us ignore as irrelevant the two mistakes Aquinas makes -- one, his error, like Aristotle's, in regarding the eye, ear, nose, skin, etc., as sense organs; the other, his consequent error in asserting that one of the special senses was subject to a natural as well as a spiritual immutation, because he supposed that the skin was a sense organ and that it suffered a natural immutation when it became hot or cold. The skin is not a sense organ; the afferent inlets of cutaneous sensibility are embedded in the skin; but the perception of hot and cold, like the perception of red and green, occur in the brain, not in the skin or the eye; and the brain does not become hot or cold, red or green, when we perceive these qualities. There is, in short, no natural immutation or alteration of the ultimate sense organ, the brain; there is only a "spiritual immutation" and this must be understood as identical with the cognitive act that occurs when a sensible form is received in cognoscitive matter. To call that act -- an act of matter, albeit cognoscitive matter -- a "spiritual immutation" is, to say the least, an unfortunate use of language. Nevertheless, what is intended is clear: the spiritual immutation of a corporeal organ is an act of matter that has intentionality, as a natural immutation does not.

      9 The differences between animal and human sense cognition are striking.
(i) Sense-perception devoid of conceptual light and so without understanding and sense-perception with conceptual light and so with understanding are worlds apart. Kant's remark that percepts without concepts are blind is true, and in man such blindness is abnormal, in animals it is the rule without exception. See DOM, pp. 334, n. 14, 348, n. 46.
(ii) In the absence of intellectual power, knowledge is not reflexive. Only man knows and, at the same time, knows that he knows. Sense cognition in animals, unlike sense cognition in man, is unaccompanied by reflexive awareness.
(iii) The functioning of signals in animal behavior can be adequately explained without any reference to meaning. One of the deepest contrasts between the sense experience of animals and that of man is the meaninglessness of the one and the meaningfulness of the other. See DOM, pp. 175-176, 178-179, 187-188, and p. 352, n. 5. However, the consideration of these differences and contrasts leads to the conclusion that sense cognition in animals (i.e., sense simpliciter) and sense cognition in man (i.e., sense eminenter are knowledge in a thinly analogical sense of the term, rather than to the conclusion that, though animals have sensory inlets and a brain anatomically similar to those in man, they do not have knowledge in even an analogical sense of that term.

      10 See Summa Theol., I, 86, 1.

      11 For a summary of Brentano's theory of intentionality, see DOM, pp. 214-215. Cf. pp. 208-210, and pp. 224-226.

      12 For an exposition of the identity hypothesis, see DOM, pp. 198, 200-207.

      13 See DOM, Chapters 13-15.

      14 See Jacques Maritain, Degrees of Knowledge (New York, 1959), p. 118, fn. 1; Cf. his Philosophie Bergsonienne, 2nd. ed., pp. 268, 276; Garrigou- Lagrange, Le realisme du principe de finalite (Paris, 1943); Yves Simon, Introduction a l'ontologie du connaitre (Paris, 1934), Ch. III, Sections 1, 2, and 3.

      15 To sum up, the Thomistic theory must posit (a) cognoscitive matter, (b) an agent intellect, and in addition (c) it also posits intentional beings as existences distinct from entitative beings. The Aristotelian theory, like the Thomistic theory, must posit (a) and (b), but it does not posit (c) because it does not need it in order to explain the existence of knowledge and to preserve its mystery.