Aquinas proceeds to consider the related question concerning the reduction of potencies to acts, i.e. the reduction of a disposition to its corresponding perfection or realization. Such an analysis will entail a twofold consideration. Aquinas maintains that an identical reduction is not obtained with both Disposition-1 and Disposition-2.
[. . .] while in the first two cases, there is potential knowledge, and while potency is such that it is able to be actualized, there is a difference, in respect of actualization, between a primary [Disposition-1] and a secondary [Disposition-2/Actuality-2] potency.
It is the case that one in potency in the secondary sense—i.e. as already possessing the habit—passes from the state of having sensations or knowledge, but not exercising them, into the state of actually knowing something here and now. And this kind of actualization differs from the other. (Commentary on the Soul, nos 362, 364)
Once this difference between these two types of reduction has been stated, the immediate problem concerns whether such a reduction, in either or both cases, is an action or a movement in the physical sense. This question has structural similarities with contemporary issues in the philosophy of mind concerning the ‘action’ status of mental acts. Both Aristotle and Aquinas were concerned about the ‘action status’ of an act of knowledge. This Aristotelian discussion in the philosophy of mind is more than merely of historical interest.
Aquinas begins this discussion by distinguishing the various senses of ‘being acted upon’. He does this in order to arrive at a clearer analysis of how these terms apply in the knowing process. In this first passage, Aquinas considers physical or material change.
Aristotle remarks that being acted upon has several meanings, like potency and act. In one sense, it implies some kind of destruction caused by a contrary quality. For in the strict sense, the state of being passive to action seems to connote, on the side of the patient, a loss of something proper to it through its being overcome by the agent. Moreover, this loss is a sort of destruction, either absolutely, as when the patient loses its substantial form; or relatively, as in the loss of an incidental form. This loss implies a contrariety in the agent, the imposition upon the patient’s matter, or being, or a contrary form from outside. In the first and strict sense, accordingly, ‘being acted upon’ means a destruction caused by a contrary agent. (Commentary on the Soul, no. 365)
This passage develops the Aristotelian account of change. It is important to note, however, that in the next passage, Aquinas offers a wider sense of ‘being acted upon’ that is different structurally from the reduction required for physical change; this passage comments on intentional or cognitive change.
In another and looser sense, the term connotes any reception of something from the outside. And as a receiver is to what it receives as a potency to its actuality; and as actuality is the perfection of what is potential; so being acted upon in this sense implies rather that a certain preservation and perfection of a thing in potency is received from a thing in act. For only the actual can perfect the potential; and actuality is not, as such, contrary to potency. Indeed the two are really similar, for potency is nothing but a certain relationship to act. And without this likeness, there could be no necessary correspondence between this act and this potency. Hence potency in this sense is not actualized from contrary to contrary, but rather from like to like, in the sense that potency resembles act. (Commentary on the Soul, no. 366; emphasis added)
This passage is important because it suggests that knowledge, although a reduction from potency to actuality, is not in itself a physical activity. It follows that Aquinas’s philosophy of mind is not reducible to physicalism. Of course, in this analysis Aquinas works within the framework of an Aristotelian definition of motion. Aristotle’s account of motion states analytically that to be moved is to undergo a reduction from a potentiality to an actuality. Aquinas, however, stresses the following difference:
- (a) an instance of knowing, which is a reduction of a knowing disposition (i.e. either Disposition-1 or Disposition-2) to its appropriate perfection;
- (b) an instance of a physical action, which is a reduction of a physical disposition to its appropriate actualization.
The force of Aquinas’s argument depends upon his claims that an act of knowledge is not contrary to its potency. Since there is an absence of contraries, it is impossible, on the Aristotelian schema for causality, for physical movement to occur. With this distinction in mind, Aquinas suggests that there is a difference between a physical change, for example, in cold water becoming hot water, and from the non-exercise of the intellectual ability to speak Hungarian by the Slavic languages professor to his actual exercise of the acquired capacity by here and now speaking Hungarian. In the former sense, when the cold water becomes hot, Aquinas argues that there is a ‘destruction’ in the physical substratum. Obviously, this is a much-amended use of ‘destruction’, for what Aquinas means is that the cold water, when it is heated, is no longer cold. The quality ‘being cold, which in Aquinas’s ontology is an accidental or incidental form, has been ‘destroyed’. A physical change of qualities always involves the destruction of the contrary quality. In this analysis, the Aristotelian theory of opposites is evidently at work. In the Metaphysics, Aristotle discusses four kinds of change, one substantial and the other three the accidental or incidental changes of quantity, quality, and place:
Change is from opposite or from intermediate to opposite. But it does not occur from just any opposite—a voice, after all, is not white—but only from contrary to contrary. There are four kinds of change: change of what a thing is, change of quantity; and changes of quality or of place. Change of what a thing is, is simple coming to be and perishing; change of quantity is growth and diminution; change of affection is alteration; change of place is motion. In each case, the change is into the appropriate contrary state. (Metaphysics, bk XII, ch. 2 (1069b5-15))
The reduction of one contrary to another is a necessary condition for physical change. This claim serves as the basis upon which Aquinas argues that knowledge is not a physical activity or movement. This account of a reduction is rooted metaphysically in Aristotelian hylomorphism.
A physical reduction in terms of act and potency entails that, when the water has been heated, the act of being cold as a fact or state of affairs is no longer an existential fact or state of affairs. Therefore, the fact, which was the water’s being cold, is no longer a fact. In Aristotelian terminology, the ‘cold fact’ has been ‘destroyed’; it has ‘perished’. Aquinas too suggests that any physical action requires a destruction or ‘perishing’ as a necessary condition. This destruction is the process of transfer from an accidental predicate to its contrary by means of some efficient agent. The passage from Aristotle’s Metaphysics indicates that this ‘destruction’ occurs in both what is called ‘substantial change’ and what is called ‘accidental or incidental change’. The former is when, for example, a block of rock maple through an appropriate heating process becomes charcoal. The latter is exemplified by the cold water/hot water example. That there are ontological problems with the substantial/accidental property distinction is not to be denied. What is important for this inquiry, however, is that, for their ontological analysis, both kinds of physical change have a movement from a contrary state as a necessary condition . On the other hand, instances of knowing encompassing sense perception, concept formation, and concept exercise are not involved with a reduction to a contrary state. It is on this ground that Aquinas maintains his claim that knowledge is a ‘perfection’ rather than an action. This solution is grounded in Aristotelian categories of explanation. Nonetheless, Aquinas was aware of this problem that has troubled contemporary philosophers. He moves beyond the limits of a materialist or a physicalist philosophy of mind. This discussion is offered as a rejoinder to Sorabji, who, among others, argues that Aristotle’s account of perception is reducible to physicalism.
In commenting on Aquinas’s philosophy of mind, Haldane reminds us that the background for understanding what Aquinas proposes is the metaphysics of Aristotle, which includes an ontology of matter and form with the corresponding structuring principles and ‘quantities of stuff given determinate natures by these principles’.13 Using these ontological categories rooted in Aristotelian theory conjoined with a theory of the mind, Haldane comments: ‘[This is] a philosophy of mind that views the intellect not as in Cartesian fashion, as an entity, but rather as a set of capacities characteristic of substances possessed of a certain type of nature. On this account, thoughts are exercises of these capacities; mental actions of the psychophysical individual.’14 In Aquinas’s philosophy of mind, the nature of the human person—what Stump and
John Haldane, ‘Brentano’s Problem, Grazer Philosophische Studien 35 (1989), 1-32.
Pasnau refer to as the ‘cognizer’—is an ontological entity characterized by sets of powers or dispositions that are actualized.
-  Nussbaum argues that the principal problems with physicalism were noted by Aristotle when hesuggested in criticizing the atomists that a thoroughgoing materialism eliminates discussion of intention-ality: ‘The different types of cognition—perceiving, imagining, thinking—are all being cashed out inexactly similar physiological terms, as the motions of certain sorts of atoms; the same is true of differenttypes of desiring . . . ’. She continues: ‘these [...] intentional features of the animal are given the same treatment as non-intentional items like blood-circulation and digestion. It is difficult to see how such anaccount could make room for the richness that is in our ordinary talk, and easy to see that the atomist doesnot much care about preserving that richness’: Martha C. Nussbaum, The Fragility of Goodness (Cambridge:Cambridge University Press, 1986), 271; ch. 9, ‘Rational Animals and the Explanation of Action, is a finetreatment of intentionality issues.