The Use of Psychology

Here is the term paper which I wrote for my class on the "De Anima," entitled "Utilitas Psychologiae: An Investigation Into the Usefulness of the Science of Soul for the First Philosopher"

With characteristic swiftness and lucidity, St. Thomas draws out of the prooemium to the De Anima the Philosopher’s intent to render his student benevolent by an exposition of the utility of the science of soul.[1] While it may seem odd that one speculative science is useful to another, psychology is so, for, “‘It gives occasions to all other notable parts of philosophy.’”[2] One most eminent part is first philosophy, for, “we are not able to come to knowledge of the divine and highest causes except by those which we first acquire of the power of the intellect.”[3] Naturally one asks: how exactly does psychology accomplish this? In reply, our inquiry will take three parts. First, the question will be determined more precisely. Second, from these precisions, the road from psychology to first philosophy will be found out. From this, an instance of such an “occasio” will be advanced: the psychologist develops the notions of potency and act as received from the general definition of motion[4] in his investigation of the grades of living things. This road of investigation leads him to the doorstep of first philosophy.


St. Thomas’ only suggestion about to the nature of the occasio provided to first philosophy is preparation to know divine and highest causes. By examining the other occasiones we can understand this one more fully.[5] First, for ethics, a lack of knowledge of the powers of the soul leads to an imperfect knowledge of virtue, for the excellence of these powers is integral to the account of virtue.[6] However, only those parts “[are] to be used” that show “that a certain part of the soul is rational,” i.e., capable of the command required for voluntary action, and “a certain part irrational . . .”[7] and thus capable of obedience. Details such as the rational or real separation of the powers can be ignored. Such imprecision is fitting, for ethics requires only factual knowledge of the powers’ accounts to teach human happiness.[8] Second, since the greater part of nature is ensouled[9] and soul is the principle and source of movement, physics as a speculative science requires psychology as a perfective part. Therefore, generally, an occasion provides beginnings to another science according to the scientific mode of such a receiver.

An explicit connection between psychology and first philosophy is found in St. Thomas’ prooemium to De Sensu. In comparing the general study of soul (the most abstract) to the posterior studies in biology that consider soul as enforming body and the various species of living beings, which are more concrete, and hence more particular,[10] St. Thomas excepts one grade of living being from this more concrete mode of study:

However, of these [grades of living beings], the intellect certainly is the act of no part of the body, as is shown in De Anima III. Whence, it cannot be considered through concretion or application to body or to some corporeal organ, for its greatest concretion is in the soul. Moreover, its highest abstraction is in the separate substances, and therefore Aristotle did not write, besides the De Anima, a book on the intellect and the intelligible (or if he had done so, it would not pertain to natural science, but rather to metaphysics, to which the consideration of separate substances belongs.)[11]

While the term ‘metaphysics’ is used here, and not first philosophy, this difference is nominal.[12] This passage, then, indicates that the proof of the human intellect’s immateriality is the beginning (in some way) of another science, for psychology cannot treat of separable being within its own scientific formality. Hence, the road psychology takes to arrive at this point is one aspect of its utility.

To understand the nature of this road, we must recall the difference in the mode of definition between physics and metaphysics. Physics studies beings in matter and motion and defines in a corresponding mode, while metaphysics knows being qua being and abstains from matter and motion as such in its mode of defining.[13] Further, physics demonstrates through all four causes, but metaphysics though only three.[14] Since man knows corporeal things first, and only those comprehensively,[15] the principles of his knowledge of such things (definitions) are at first insufficient as principles of knowledge of beings existing apart from matter or motion. For psychology (and consequently the psychologist) to provide occasions to first philosophy,[16] it must extend its principles. As St. Thomas’ prooemium to the De Sensu implies, this occurs along with the scientific discovery of grades of living beings that require such extensions in order to be known: the vegetative, sensitive, and intellectual souls.

Now, among the inferior living things (as opposed to separate ‘living’ beings) there is a two-fold manner of being: one is material, in which things are contracted to a single species; the other is immaterial, meaning that such things can receive other species in addition to their own.[17] This immaterial being is itself two-fold:

. . . for one is completely immaterial, namely intelligible being, for in the intellect a thing has being both without matter and the individuating conditions of matter, and also apart from a corporeal organ. However, sensible being is a mean between the two, for in sense a thing has being apart from matter, yet apart from neither the individuating conditions of matter nor apart from a corporeal organ, for sense is of particulars, while the intellect is of universals. And it is with respect to this twofold being the Philosopher says in the third book of this [treatise] that the soul is in a certain way all things.[18]

Hence, there are two levels above material living being—to which the vegetative soul is limited—and three grades in all. The vegetative soul retains all three conditions: an enmattered form, consequent individuating conditions, and an organic body. Sensitive material souls can receive additional sensible forms without matter, but still receive according to individuating conditions and with organs. The intellectual soul, however, “a form of matter but not a material form,”[19] receives being and additional forms apart from all three conditions.[20] Granted that this mode of ranking is metaphysical (for to consider an immaterial order among beings as such falls under a metaphysical mode of definition), nonetheless, it indicates the two key scientific moments in the road from psychology to first philosophy: the consideration of potency and act as belonging to sensation (DA II.5), and the analogous discussion about the intellect (DA III.4).[21]


The first, De Anima II.5, serves as preamble to the treatise on the sensitive soul. St. Thomas marks three stages in the argument: first, it is shown that the senses admit of being in potency and in act; second, precisions are advanced by illustration from the intellect concerning the manner of reduction from potency to act; third, these precisions are applied to sensation.[22] These can be treated in four parts: first, the reason that the extension must be made; second, the preparation to understand the extension; third, the distinction itself; and finally, how this leads to the first grade of immaterial being.

What demands this extension as solution is the problem that entangled the ancient physicists, who attempted to explain sensation by alteration. To approach a resolution, Aristotle first what notes most characterizes the case: “Sensation occurs to something being moved and suffering.”[23] The opinions of his predecessors are mentioned to frame the query for the sake of the learner: “Moreover, some even say that like suffers by like,”[24] which he states is only qualifiedly true, alluding to De Generatione I.7.[25] This position of the ancients concerning alteration generally serves as a point of departure for the more particular problem of alteration in sensation, for it specifies to “like is sensed by like.”[26] Now, alteration strictly speaking is change from one qualitative species to the intermediate or contrary within the same genus: what is cold becomes warm or hot.

Given this beginning, in what way is sensation alteration? The ancient view, that sensation is alteration simply, where a like thing senses its like, cannot be true for this reason at least, that the need for something beyond the sense powers to cause actual sensation would be obviated: the sense power, like itself, would cause actual sensation of itself.[27] Since some otherness is required, the senses are in potency towards their objects. Furthermore, they are only intermittently in act, for a sleeping man and a waking man are both called sensing, the former in potency and the latter in act. This conclusion (that the senses admit of both act and potency) raises the issue of extension. How are the senses said to be in act when they suffer something from the sensible object? Recalling the received definition of motion from the Physics (“. . . as was said in another place.”), Aristotle points out that sensation can be called a sort of motion, although he insists that this is a preliminary and imprecise way of speaking.[28] St. Thomas notes that, “by this that [Aristotle] says ‘First,’ he indicates that after a certain while he will supply some things to show how sense becomes actual.”[29] Aristotle’s intention here is that “concerning both potency and act a distinction must be made, for now we are speaking of them simply.”[30] Aristotle thus warns his student to be attentive.

The preparation for this distinction is the second step in Aristotle’s argument (417a21–417b16). This is accomplished “using the intellect as an example.”[31] This example, by considering how men speak about knowers and knowing, distinguishes three stages: the ability to know that follows upon human nature, the state of actual consideration, and the in-between state, or the acquired ability to consider knowledge. Thus, a man is at first ignorant of the science of grammar, but able to learn it. Once he learns it, he can consider it at will. This yields the traditional “triple scheme”[32] of first and second potency and actuality. However, since the science of grammar is preserved in the active grammarian, these three stages are unlike the act and potency involved in substantial and accidental (take alterative) change. In the latter case, the second potency of a subject is the disposition of the present alterable quality, which is destroyed when altered: a cold thing’s potency to be hot, once actualized, is gone, and can only be regained by return to the contrary. By contrast, the habit of science is a disposition which, when in act, is not lost in comparison to its activity. Not thinking is not a strict contrary to thinking. The habit principles consideration, and it merely progresses “into itself.”[33]

Hence, while “one sort” of alteration “is a certain corruption by the contrary, the other however is rather [a] a saving of it that is in potency by that which is in act and [b] thus by a similar thing just as potency has itself to act.”[34] With this obscure sentence Aristotle at once reveals the difference and similarity involved. The difference [a] is this: “that which is in act” (a grammarian considering) preserves “it that is in potency” (the habit of grammar), unlike the potency to be hot, which is exhausted when actualized. The similarity [b] is that the first still bears to the second the relationship of potency to act. The difference obtains the extension, while the similitude retains the account to motion. Whence it is not alteration strictly, but rather another kind of alteration.

The third and final step (417b6–418a6) St. Thomas describes thus, “What [Aristotle] had said about the intellect he fits to the senses.”[35] After the determination is applied, it is clarified by giving exceptions. The application is as follows:

The first change of the sensitive, however, comes about by generation. But when a thing is generated, it has sensing already, just as knowledge; which [sensing] however according to act is said similarly to considering.[36]

In the analogy, the habit of knowledge and its actual consideration align with the generated animal soul (with its sense power) and the exercised sense power. As the ability to sense is not lost during sensation, the extended, qualified notion of alteration fits, for “the sensitive in potency is like the sensible already in act, as was said.”[37]

This conclusion is qualified, for sensation concerns particulars and science universals. Additionally, the former are “outside the soul,” while the latter are “in a way inside;”[38] hence the former objects cannot be actually considered at will as the latter can. Therefore, while Aristotle actually achieves in DA II.5 three distinctions in alteration (namely among the material, sensitive, and intellectual), the difference between intellect and sensation must be made clearer, “namely in the third book where [Aristotle] treats of the intellect and of the comparison of the intellect to sense.”[39]

However, due to this last mark, an objection arises. The way in which the extension has been made seems circular, for psychology’s consideration of the senses is a preamble to the consideration of intellect—what is determined about sensation is later used to understand intellection (DA III.4, 429a13ff). However, no vicious circle exists. At this point in the scientific order of psychology the difference between intellect and sensation has not been argued for (this comes at III.3, 427a17-b14). Whence, the experience used to manifest the difference between material alteration and sensitive operation need not be known distinctly in itself, only better known to us. Now, the experience of learning and considering is more known to us, for it occurs at will and is interior. Thus Aristotle uses it in the extension, but marks these very differences at the end of his treatment. When the extension is used to examine each particular sense, these examinations start from other more known experiences. Thus, no vicious circle obtains.

It remains to show how these distinctions lead to the first grade of living being that St. Thomas calls immaterial. Now, in the De Anima’s subsequent particular considerations of each sense, the account of each power is determined via its object. Whence, each power is of a sort that is actualized by its proper object in the mode of that second actuality which preserves the power: the reception of the sensible species is such that it preserves the potency ordered to such reception. However, this reception must take place without the matter of the object acting upon the sense power, for such a manner of material alteration was excluded by the arguments in II.5. The ordinary mode of alteration, as experience shows, consumes the potency towards the contrary once the contrary is led into act. The sensitive mode of alteration must involve a different kind of potency since this does not occur. In view of this, Aristotle begins his summary of the treatise on the external senses by observing that, generally, “sense is what is receptive of the species without the matter . . . .”[40]

This is clear also from St. Thomas’ concern in the same place, for, “it seems that this is common to all passion,” namely to be receptive of the form without the matter:[41] for even “air does not receive matter from the fire acting upon it, but form.”[42] However, the mode of reception of form depends upon the disposition of the receiving matter. The reception of sensible qualities in things and in sense powers is thus differentiated:

. . . the senses receive the form without the matter, because the form has a different mode of being in the sense [power] and in the sensible thing, for in the sensible thing it has natural being, but in the sense [power] it has intentional or spiritual being.[43]

Hence, reception “without the matter” must be taken according to another manner of material disposition. The first level of immaterial being is thus established, for metaphysics (in its mode of definition) can name such reception immaterial.[44] Psychology (in its mode) must name this reception with reference to matter, i.e. as regarding the preservation of the potency in question, defining the intrinsic formal cause of the enmattered power by denomination from its extrinsic formal cause: the object.[45]

Since the account of intellect is preliminarily determined through a comparison to sensation, the claimed extension of potency and act regarding intellection is made easily. With this extension comes the second grade of immaterial being. The beginning of this further distinction is DA III.4, the treatment of the possible intellect. The agent intellect will be excluded from the current consideration, for whatever applies to the possible intellect is found even more so in the agent, for the agent is nobler than the patient.[46] Further, the detailed argument for the difference between sensation and intellection will be assumed (DA III.3, 427a17-b14).[47]

The first half of DA III.4 (429a10-b9) “shows the nature of the possible intellect”[48] in two parts: first, the nature of the power, and second, “how it is reduced to act.”[49] While intellect occupies Aristotle from III.4-7, he wastes no words up front; he “reaches these determinations about the mind and its operation by reference to its object” namely all things, before the discussion “becomes more specific,” later on (429b10ff).[50] Since the nature of the intellect is obtained from its object within the first half of III.4; this part can be focused on while maintaining completeness. It has three sections:

[Aristotle] first proposes the likeness of intellect to sense; second, from such likeness he concludes to the nature of the possible intellect. [T]hird, he shows the difference between intellect and sense from the things he had proved of the intellect . . .[51]

With an air of déjà vu, the intellect’s similitude to sense serves as the entry-point to understanding its nature. This amounts to a simple analogy: “[J]ust as the sensitive is to sensibles, likewise is the intellective to the intelligibles, for either one is in potency to its object and receptive of it.”[52] However, and St. Thomas reminds the reader of this (“[E]ven sensing, as was said above in Book II, is not properly a passion.”[53]), the ‘suffering’ of the intellect must be understood analogously; further, as sensation and intellection differ, this analogous sense of passion may require distinction.

This second distinction is confirmed once the nature of the possible intellect is shown. In short, “because [the intellect] understands all things, it is unmixed.”[54] Since the reach of mind is so broad, as power it must be a proportionate receptacle, lacking in any incumbent species. Hence, the intellect “is not something bodily or mixed with bodily things . . . nor does it have a corporeal organ,”[55] for in either case its cognitive range would be hindered.

This unmixed nature of the intellect allows the difference between it and the senses to be shown, which provides the complete account of the two grades of immaterial being. For the senses powers, as acts of organs, have a certain “annexed material change,”[56] and are thus impaired in their reception of lesser sensibles after having received an intense sensible species (think of the ‘ghost colors’ seen after staring at bright objects). Further, they cannot sense the excessively sensible without damage or destruction. The intellect, however, understands lesser intelligibles better, and not worse, “when it understands something greatly intelligible.”[57]

This difference between sense and intellect in the reception of their respective objects (borne out by experience) indicates a difference in their ‘material’ dispositions. On the one hand, the preservation of the potency of the sense powers is limited or destructible (noise can temporarily or permanently deafen); on the other hand, the preserved potency of the intellect is not. Hence, “lest some believe that there is the same grade of impassibility in sense and intellect,”[58] this shows that “since [the intellect] lacks an organ, it is thus passible neither per se nor per accidens.”[59] This distinct grade of reception corresponds to the second immaterial grade of being indicated by St. Thomas, for, since the intellect is immaterial, it must receive other forms accordingly.


We now see how the road through psychology provides occasions for first philosophy. Insofar as psychology establishes the specific account of the sensitive and intellectual souls, and realizes an extension of the physicist’s notions of potency and act, it touches upon grades of being that it can only name as less passible than its first notion of material change. However, the metaphysician or first philosopher, who defines in an immaterial mode, can name these as diverse grades of being as being, as St. Thomas does: they comprise a two-fold immaterial being, intelligible and sensible.

Aristotle, in his prooemium, does not render his students benevolent in vain. Psychology indeed has its pride of place among the parts of physics. Just as the general physicist perfects his science by demonstrating the First Mover, which he shows to be “partless”[60] and outside his subject genus, so also the general psychologist reaches the height of his considerations when proving the immateriality of the intellectual soul. While the former demonstration shows the existence of a complete substance, and the latter of a substance qualifiedly complete, these qualifications can only be given by metaphysics, for its purview is substance as such. The metaphysician also sees that the physicist reaches a total separation from matter and a perfect distinction between metaphysics and physics, but the psychologist only a partial one, as the human soul is an incomplete substance. Nevertheless, the psychologist’s demonstration is somewhat superior, for it shows the formal cause of a separate being that is still part of physics’ subject, even if this very demonstration also shows that man is a part of the subject as a “limit” is part of the thing.[61] The philosopher locates himself, via soul, “on the border of corporeal and separate substances.”[62] He simultaneously reaches wisdom’s doorstep, but with “equipment” sufficient to continue “the journey to the whole of truth.”[63]

[1] See St. Thomas Aquinas, Sentencia Libri de Anima, c.1 (Roma – Paris: Commissio Leonina – J. Vrin, 1984) t.45, v.1, p.3-7. I will call this science of soul ‘psychology,’ meaning primarily that integral part of natural science that first studies the soul in itself “as if in a certain abstraction.” See St. Thomas, “. . . primo quidem considerauit de anima secundum se quasi in quadam abstractione . . . . Prima igitur consideratio continetur in libro De Anima . . .” Sentencia Libri de Sensu et Sensato (Roma – Paris: Commissio Leonina – J. Vrin, 1985) (45/2.4:40-1, 47-8).

[2] St. Thomas, SLDA, “‹‹Ad omnes enim partes philosophie insignes dat occasiones.››” (Leon.45/1.5:117-8); Gauthier notes that St. Thomas is quoting Themistius, see fn.5 below.

[3] Ibid., “Quia . . . non possumus deuenire in cognitionem diuinorum et altissimarum causarum nisi per ea que ex uirtute intellectus primo acquirimus.” (Leon.45/1.5:118-122).

[4] This definition is established by the general introduction to physics, i.e. the properly first, holistic, and general study of mobile being (Aristotle’s Physics).

[5] St. Thomas follows other commentators in detailing such occasions in Aristotle’s prooemium, although his specifics vary somewhat from others in the tradition. Themistius, comparing the habit of psychological science to equipment needed on the journey to all truth, holds that, “. . . if [the soul] knows itself, it is credible on other [matters] too; but if misled about itself, on what else could it be considered credible?”a He gives the same uses of psychology to ethics and natural science, and adds only that the soul may be the source of movement “for all bodies,” but does not mention here his view on the intellect. Averroes distinguishes between a strict utility towards physics and that offered other sciences: towards concrete biology, psychology is not merely useful, but necessary, whereas it provides assistance (iuvamentum) to other sciences in three ways. One is as the “noblest” part of a science, due to the nobility of its object. Another is a “common help” since it provides knowledge of causes. He also notes the help provided to moral science and to divine science, by giving beginnings: “Divine science however, takes from it the substance of its subject. Indeed it will be shown here, seeing that the separate forms are intelligences . . .”b

a Themistius, On Aristotle’s On the Soul, trans. R. B. Todd (New York: Cornell University Press, 1996) 15 (1,24). b “Divinus autem suscipit ab ea substantiam sui subiecti. Hic enim declarabitur quoniam forme abstracte sunt intelligentie . . .” Averroes, Commentarium Magnum in Aristotelis De Anima, ed. F. Stuart Crawford (Cambridge, Mass.: Medieval Academy of America, 1953) (5:28-30).

[6] St. Thomas, SLDA, “Si uero attendatur quantum ad moralem, non possumus perfecte ad scienciam moralem peruenire nisi sciamus potenciis anime; et inde est quod Philosophus in Ethicis attribuit quaslibet uirtutes diuersis potenciis anime.” (Leon.45/1.6:122-6). See Aristotle, Nicomachean Ethics, 1102a16-31.

[7] St. Thomas, Sententia Libri Ethicorum (Romae: Ad Sanctae Sabinae, 1969), “est utendum . . . quod quaedam pars animae est rationalis, quaedam irrationalis . . . .”(Leon.47/1.69:103-4).

[8] See Ibid., (Leon.47/1.68:72-85).

[9] Following the classical view that the realm of nature (phusis) is limited to the sub-lunar sphere. Therefore, of such species, the majority of them are alive. To investigate a modern recovery of this position would be beyond the scope of this paper.

[10] See St. Thomas, SLDS, c.1, (Leon.45/2.4:41-7).

[11] Ibid., “Horum autem intellectus quidem nullius partis corporis actus est, ut probatur in III De anima; unde non potest considerari per concretionem uel applicationem ad corpus uel ad aliquod organum corporeum: maxima enim concretio eius est in anima: summa autem eius abstractio est in substanciis separatis; et ideo preter librum De Anima Aristotiles non fecit librum de intellectu et intelligibili (vel si fecisset, non pertineret ad scientiam naturalem, sed magis ad methaphisicam, cuius est considerare de substantiis separatis.)” (Leon.45/2.5:68-79).

[12] See John F. Wippel, Metaphysical Themes in Thomas Aquinas (Washington DC: CUA Press, 1984) 55-67, “‘First Philosophy’ According to Thomas Aquinas,” where he argues that divine science’s various names signify one science from diverse aspects or accounts. The consideration of the human intellect as immaterial has the notion of “metaphysics” insofar as it is posterior to physics in the order of sciences with respect to us, and the notion of “first philosophy” insofar as it is a separate being (albeit the lowest and only incompletely immaterial).

[13] See St. Thomas, Super Boethium de Trinitate, q.5, a.1, 2, &4; also SLDA, I.2, (Leon.45/1.11-2); also De Unitate Intellectus contra Averroistas, (Roma: San Tommaso, 1976) c.1, (Leon.43.297:514-8).

[14] The material cause is considered only under the account of potency, which, along with act, divides being per se, and thus falls under the scope of metaphysics.

[15] See St. Thomas, Summa Theologiae, Ia., q. 84, a. 7, c., “Huius autem ratio est, quia potentia cognoscitive proportionatur cognoscibili . . . Intellectus autem humani, qui est coniunctus corpori, proprium obiectum est quidditas sive natura in materia corporali existens.” (Leon.5.325). See also ST, Ia., q.88, a.2; Expositio Super Boethium De Trinitate, q. 1, a. 3, c.

[16] It must be recalled that psychology is properly a part of physics (see DA I.1). Hence, it considers soul insofar as it is a form of matter and principle of motion. How this extension retains the unity of psychology within physics will become clear. Also, it must be kept in mind that the physicist’s naming and knowledge of corporeal things that have greater degrees of immateriality is, strictly speaking, negative.

[17] See St. Thomas, SLDA, II.5, (Leon.45/1.88:55-70).

[18] Ibid., “. . . nam quoddam est penitus inmateriale, scilicet esse intelligibile, in intellectu enim res habens esse et sine materia et sine condicionibus materie indiuiduantibus et etiam absque organo corporali; esse autem sensibile est medium inter utrumque, nam in sensu res habet esse absque materia, non tamen absque condicionibus materie indiuiduantibus neque absque organo corporali; est enim sensus particularium, intellectus uero uniuersalium; et quantum ad hoc duplex esse dicit Philosophus in III huius quod anima est quodam modo omnia.” (Leon.45/1.88:70-83)

[19] B. C. Bazan, “The Human Soul: Form and Substance? Thomas Aquinas’ Critique of Eclectic Aristotelianism” Les Archives d'histoire doctrinale et littéraire du Moyen Âge, 64 (1997): 95-126. See St. Thomas, Quaestiones Disputatae de Anima (Roma – Paris: Commissio Leonina, 1996) q.1, 2. Bazan’s thesis is qualified by methodological studies; see M. J. Sweeney, “Soul as Substance and Method in Thomas Aquinas’ Anthropological Writings,” Les Archives…, 66 (1999): 143-187.

[20] How the intellectual soul is receptive of being in the sense meant here is proved in metaphysics. It does so receive, for it is in potency towards its act of being (esse). See St. Thomas, QDA, q.6, “Cum igitur anima sit quedam forma per se subsistere potens, est in ea compositio actus et potentie, scilicet esse et quod est, non autem compositio materie et forme.” (Leon.23.51:255-8). The major premise is that all subsistent forms have a composition of potency and act, excepting God.

[21] In the sequel, the two central methodological principles of physics will be at work (See Physics, I.1, 184a17-24 and De Anima, II.4, 415a15-24, respectively). The first is a progression from the more to less general. Psychology assumes the general definition of motion (Physics III.1-3) and must determine how soul is such a principle of the motion in living beings, a more specific kind of mobile being. Second, the account of the essence and powers of this soul must come through that of objects and acts. Thus precisions are achieved from consideration of the objects and operations of sensation and intellection, which require a subject that does not principle motion in the usual sense.

[22] St. Thomas, SLDA, “. . . ostendit quod sensus sit in potencia; secundo quod quandoque est in actu . . .” (Leon.45/1.108:39-40); “. . . distinguit potenciam et actum et ostendit quomodo diuersimode aliquid educatur de potencia in actum, utens exemplo intellectu . . .” (Leon.45/1.110:5-7); and “. . . ostendit propositum circa sensum . . .” (Leon.45/1.110:8).

[23] Aristotle, De Anima, 416b33-34, “Sensus autem in moueri aliquid et pati accidit . . .” (Leon.45/1.107). We shall use the translatio nova of De Anima, as we are attempting to follow Aristotle through St. Thomas.

[24] Ibid., 416b35, “Aiunt autem quidam et simile a simili pati.” (Leon.45/1.107).

[25] See Aristotle, De Generatione et Corruptione, 323b1-324b24. St. Thomas notes, as Aristotle does in DA 417a17-21, that it is qualifiedly true for “id quod patitur a principio dum patitur est contrarium agenti, set in fine quando iam est passum est simile; agens enim agendo assimilat sibi paciens.” (Leon.45/1.108:33-6). Commentators both ancient and modern agree to the reference: Gauthier includes Themistius, Averroes, St. Albert, and two anonymous ones; see also M. Burnyeat, “De Anima II.5,” Phronesis, 47 (2002): 38. “It is entirely appropriate, then, that Aristotle’s next move . . . is to send us to De Generatione et Corruptione I 7 for a general account of [the ancients’ mistake.]” Burnyeat laments that a lack of attention to cross-references has caused many misinterpretations, see 31-2.

[26] St. Thomas, SLDA, “. . . quod simile simili sentitur.” (Leon.45/1.109:120)

[27] As a sign of the unity of this portion of psychology with the more general treatment of alterative motion, we can notice with Burnyeat (“De Anima II.5,” 39-40) the similarity of Aristotle’s second argument presented here (417a3-6) with that in De Generatione at (323b21-3), against the more general position.

[28] Aristotle, DA, 417a16, “. . . sicut in alteris dictum est.” (Leon.45/1.107). See Aristotle, Physics III.1, 201a11-2. Motion is the actuality of what exists in potency as such, which entails that it is the act of the imperfect, for it exists only while the potency of the subject is being reduced into act without remainder. Indeed, the burden of the current argument is to establish that that ‘motion’ which is sensation is the act of something perfect, i.e. whose potency remains or endures.

[29] St. Thomas, SLDA, “Per hoc autem quod dicit ‹‹Primum››, significant quod quedam alia postmodum subdet ad ostendendum quomodo sensus fiat in actu.” (Leon.45/1.109:114-117).

[30] Aristotle, DA, 417a21-22, “Diuidendum autem et de potencia et actu est. Nunc enim simpliciter dicimus que habemus de ipsis.” (Leon.45/1.110)

[31] St. Thomas, SLDA, “. . . utens exemplo intellectu . . .” (Leon.45/1.110:7).

[32] Burnyeat, “De Anima II.5,” 48.

[33] Aristotle, DA, 417b6, “. . . in ipsum . . .” (Leon.45/1.110).

[34] Aristotle, DA, 417b2-4, “. . . aliud quidem corruptio quedam a contrario, aliud autem salus magis eius quod potencia ab eo quod est actu et simili sic sicut potencia se habet ad actum.” (Leon.45/1.110).

[35] St. Thomas, SLDA, “. . . quod dixerat de intellectu adaptat ad sensum.” (Leon.45/1.114:4).

[36] Aristotle, DA, 417b16-18, “Sensitiui autem prima quidem mutatio fit a generante; cum autem generatum est, havet iam sicut scienciam et sentire; quod autem secundum actum similiter dicitur ipsi considerare.” (Leon.45/1.114).

[37] Ibid., 418a3-4, “. . . sensitiuum potencia est quale iam actu sensibile, sicut dictum est.” (Leon.45/1.114). It is absolutely crucial to recognize here that it is the capacity to see, hear, etc., that is shown to be a preserved potency, and not whatever concomitant material changes are annexed to such acts (retinal chemical alterations, eardrum vibrations). The sensitive experience and objects themselves are in question, not their corporeal underpinnings. Thus, this conclusion is prior to the issue of concomitant material changes, much debated by Thomists and Aristotelians alike, for the sense powers, certain forms, must be understood before their matter (organs) following the proper order of physics: the less to the more concrete.

[38] St. Thomas, SLDA, “. . . sunt extra animam. . . . quodam modo sunt in anima.” (Leon.45/1.115:46, 49).

[39] Ibid., “. . . scilicet in III ubi agetur de intellectu et de comparatione intellectus ad sensum.” (Leon.45/1.115:62-3).

[40] Aristotle, DA, 424a18-9, “. . . sensu quidem est susceptiuus specierum sine materia . . .” (Leon.45/1.168).

[41] St. Thomas, SLDA, “. . . uidetur hoc esse commune omni pacienti . . . non enim aer recipit ab igne agente materiam eius, set formam.” (Leon.45/1.169:18).

[42] Ibid., “(Leon.45/1.169:23-4).

[43] Ibid., “. . . sensus recipit formam sine materia, quia alterius modi esse habet forma in sensu et in re sensibili: name in re sensibili habet esse naturale, in sensu autem habet esse intentionale siue spirituale . . .” (Leon.45/1.169:52-6).

[44] It seems that metaphysics does so only in its peculiar mode of sapiential retrospection: in this comparison, the intellect (a wholly immaterial cognitive power) is taken as the first analagate, and the senses are compared to it insofar as they fall short of its spiritual mode of intentional reception.

[45] While “the object necessarily takes the aspect of agent and end,” insofar as its corresponding power is passive or active, respectively, it is nevertheless included under the aspect of extrinsic formal causality, for it does not treat of the existence of things (as do the efficient and final causes) but of their essence: “This specification will therefore obtain in the line of formal causality, but this will not be intrinsic formal causality, for the objects are exterior to the acts and powers, and the acts, in their turn, are exterior to the powers. It remains that it is but a sort of causality, the extrinsic formal cause.” Stanislas Cantin, Précis de Psychologie Thomiste, (Québec: Les Presses Universitaires Laval, 1960) 35-6, “[Cependant, il importe de remarquer que si] l’objet se prend nécessairement du côté de l’agent et de la fin…. Cette specification se tiendra donc dans la ligne de la causalité formelle, mais ce ne sera pas de la causalité formelle intrinsèque, car les objets sont extérieurs aux actes et aux puissances, et les actes, à leur tour, sont extérieurs aux puissances. Il ne reste qu’une sorte de causalité, la causalité formelle extrinsèque.”]

[46] See St. Thomas, SLDA, (Leon.45/1.219-20:64-86).

[47] We can note, however, that the argument depends upon the fact that there are some objects (judgments, opinions, and understood simples) that cannot be accounted for by the sensitive powers; therefore, some other power is required.

[48] St. Thomas, SLDA, “. . . ostendit naturam intellectus possibilis.” (Leon.45/1.202:24-5).

[49] Ibid., “. . . quomodo reducatur in actum . . .” (Leon.45/1.201:25-6). These two parts correspond to the first chapter and first part of the second chapter, respectively, of SLDA III.

[50] Kurt Pritzl, “The Cognition of Indivisibles and the Argument of De Anima 3.4-8,” Proceedings of the American Catholic Philosophical Association 58 (1984): 141. St. Thomas agrees: see SLDA 216:81-5. The position of this reference requires that the first half of DA III.4 is meant, as Gauthier notes.

[51] St. Thomas, SLDA, “. . . primo proponit similitudinem intellectus ad sensum; secundo ex huiusmodi similitudine concludit naturam possibilis intellectus . . . tercio ostendit ex hiis que de intellectu probauerat differenciam inter intellectum et sensum . . .” (Leon.45/1.202:56-61).

[52] Ibid., “. . . sicut se habet sensitiuum ad sensibilia, similiter se habere intellectum ad intelligibilia, quia utrumque est in potencia ad suum obiectum et susceptiuum eius.” (Leon.45/1.202:87-90).

[53] Ibid., “. . . nam sentire, ut supra in II ditum est, non proprie pati est . . .” (Leon.45/1.202:76-7).

[54] Aristotle, DA, 429a18, “. . . quoniam omnia intelligit, inmixtum esse . . .” (Leon.45/1.201).

[55] St. Thomas, SLDA, “. . . non est aliquid corporeum uel commmixtum ex rebus corporalibus . . . neque habet organum corporale . . .” (Leon.45/1.203:94-6).

[56] St. Thomas, QDA, q.13, c., “. . . materialem immutationem annexam . . .” (Leon.24/1.118:309-10).

[57] Aristotle, DA, 429b3, “. . . cum intelligit aliquid ualde intelligibile.” (Leon.45/1.201). Generally, an example of this can be found whenever the mind rests in a cause, for causes are more intelligible than their effects, and the effects are better understood in them. An example is when Aristotle arrives at the definition of place in Physics IV (no pun intended). This understanding not only dispels the difficulties (confusions, a kind of lesser intelligible) concerning the definition of place, but it also allows local motion (less intelligible in itself experientially) to be understood scientifically. Whence, “greatly intelligible” must be taken to mean what is better known in itself, not what is better known to us. The intelligibles notior naturae are bright lights that shed light on and intensify the lesser lights that guide our first, obvious experiences.

[58] St. Thomas, SLDA, “Ne ergo aliquis crederet quod in eodem gradu inpassibilitatis esset sensus et intellectus . . .” (Leon.45/1.205:243-4).

[59] Ibid., “. . . cum organo careat, under nec per se nec per accidens passibilis est.” (Leon.45/1.205:250-1).

[60] Aristotle, Physics, translated R. Glen Coughlin (South Bend: St. Augustine’s Press, 2005) 190.

[61] See St. Thomas, De Unitate Intellectus, “Therefore the limit of the consideration of the physicist concerning forms is in forms which are in matter in a certain way, and in another way not in matter; for such forms are on the border of the separate and material forms.” [“Terminus ergo considerationis phisici de formis est in formis que sunt in materia quodammodo, et alio modo non in materia; iste enim forme sunt in confinio formarum separatarum et materialium.”] (Leon.43.297:518-522).

[62] St. Thomas, QDA, q.1, “. . . in confinio corporalium et separatarum substantiarum [constituta].” (Leon.24/1.10.340-1). Compare De Unitate Intellectus, fn.61 above.

[63] Themistius, On Aristotle’s On the Soul, 15.


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