On Potency and Act
In probing Empedocles’s work, Aquinas interprets this principle in terms of potency and act. The sense faculty is able to ‘become’ the object in the external world in an immaterial, intentional manner. Empedocles’s physicalism, so Aquinas suggests, rules out the possibility of an intentionality theory. In his On Spiritual Creatures, Aquinas refers to Empedocles and the ‘Like knows like’ axiom:
The early philosophers asserted that the knowing subject should be of the same nature as the thing known. Hence Empedocles said: ‘We know the earth through earth and the water through water’. But to rule this out, Aristotle asserted that the knowing power in us, according as it is in potency, is void of the nature of the things that can be known. Thus, the pupil of the eye, for example, is void of colour. But yet the sense in act is the thing sensed in act, inasmuch as the sense is put in act through being informed by the sensible species; and by the same reasoning, the intellect in act is the thing understood in act, inasmuch as it is informed by the intelligible species: ‘For a stone does not exist in the soul, but the species of a stone,’ as Aristotle himself says. Now the reason why something is intelligible in act is that it is separated from matter. And consequently, he says: ‘In those things which are without matter, the understanding subject and the thing which is understood are the same.’ Therefore the understanding angel need not be the same in substance as the understood angel, if they are immaterial. But the understanding of the one must be informed by a likeness of the other. (On Spiritual Creatures, art. 8)
In this discussion, there appears to be a twofold problem noticed by Aquinas in which the concepts of act and potency are used: (a) The mental act of direct awareness itself; (b) the knowing faculty or power as a disposition. From the passages quoted above, it appears that Aristotle and Aquinas consider both faculty and mental act, whereas Empedocles considered only the mental act. The act/potency distinction, however, does pertain to knowing faculties or powers, which is the second proposition. In that proposition, the knowing power is considered as a ‘disposition’ or ‘potency’ capable of ‘intentionally becoming’ another thing. However, this second set of issues involving knowing faculties did not bother Empedocles; he appears to have been concerned only with the mental act of sensation itself, not the mental faculty of sensation. Early on in his Commentary, Aquinas, in responding to Empedocles, offers the important distinction between the mental act of awareness, the sense organ, and the knowing faculty. Empedocles does not distinguish the sense organ from the sense faculty.
In regard to this passage, moreover, Aquinas and Aristotle suggest that ‘intentional becoming’ is quite different from ‘material becoming’. If ‘Like knows like’ were only another instance of ‘material becoming’, then this would rule out a priori any form of ‘intentional becoming’. Once again, Aquinas uses an intentionality theory to undercut a physicalist account of mind. The two propositions are not in conflict. They do indicate, moreover, that Aristotle and Aquinas were not only commenting upon a historical position in sensation and perception theory. Rather, they elaborated upon and developed their own theory. Therefore, in the analysis of ‘intentional becoming’, the concepts of act and potency are used in two senses. The consideration of these uses demand further analysis, which will be undertaken later in this chapter.