If ‘being acted upon’ in a knowledge process is not to be taken in the sense of a physical action in the Aristotelian framework, one might rightly ask about the ontological status of the referent for this newly acquired phrase. Aquinas next considers the meaning of ‘being acted upon’ in the two senses of disposition: Disposition-1 and Disposition-2. This indicates how both can involve ‘being acted upon’ and yet not entail a physical action. Aquinas begins this analysis by considering Disposition-2:
Aristotle discusses whether the actualization of already acquired knowledge involves a being acted upon. And he first discusses the process of transit from secondary potentiality into fuller actuality; [. . .] he asserts that this movement into actual thinking is not truly passively being altered. For, as we have seen, no movement into act, as movement into act, is such. The term applies, strictly, only to the alteration of a subject from one to the other of two mutually exclusive qualities. (Commentary on the Soul, no. 367; emphasis added)
That such a reduction does not obtain in the process of going from Disposition-2/ Actuality-1 to Actuality-2 is indicated in the next passage:
But this is not what happens when a person begins to exercise her mind on knowledge she already possesses. Rather she is developing a quality already possessed. As Aristotle remarks, it is a ‘new perfection’ in her and an ‘increase in actuality’. For perfection increases with actuality.
Accordingly, if one insists on using the terms ‘actuality’ and ‘being acted upon’, it is necessary that they must be taken in a wider and less strict sense. In order to illustrate this point, he adds that it is just as inept to speak of a thinker being ‘altered’ when she actually thinks as to say of a builder that he is altered by building. (no. 367; emphasis added)
These discussions are central to Aquinas’s theory of mind. He holds that the exercise of knowledge, which is the process of going from Disposition-2 to Actuality-2, is not an instance of a physical action. Rather, it is a perfection or realization of a qualitative becoming. Aquinas goes to great lengths to claim that the exercise of knowledge is not an alteration or ‘being altered’. It cannot be an alteration because an alteration is a change from a contrary to its opposite. He argues that in going from Disposition-2 to Actuality-2, there is a complete absence of a movement or becoming from contraries. There is, on the other hand, a further developing of a quality or perfection already possessed. In reference to the ten Aristotelian categories, knowledge, for Aristotle and Thomas, belongs to the category of quality and not to the category of action. This classification depends upon the exemplification of instances from the ten Aristotelian categories.
In his Commentary on the Physics, however, Aquinas writes what might appear to deny the above analysis:
From this Aristotle further concludes universally that alteration occurs in the external senses, and in the sensibles, and in the whole sensitive part of the soul (which he says because of the internal passions). But in no other part of the soul is there alteration, except per accidens. (Commentary on the Physics, bk 7, lec. 6 (no. 925))
This passage is not, however, in opposition to the texts in the Commentary on the Soul. In the Commentary on the Physics, Aquinas considers the physiological change of a sensible object acting on a sense organ. While this is a necessary condition for an awareness of sensation, it is not sensation itself; this will be discussed in the following chapter.
In his On the Power of God, Aquinas, in considering how God affects change in the world, discusses this issue. He argues that the ‘actualization of the sense organ’ is distinct from the ‘act of the sensitive power’
For this reason, the relation, which arises from the act of the mind, cannot be in that thing. The same applies to sense and the sensible object. For although the sensible object by its own action affects the organ of sense, and consequently bears a relation to it, just as other natural agents have a relation to the things on which they act, nonetheless, it is not the alteration of the organ that perfects the act of perception, but the act of the sensitive power. (On the Power of God, bk III, q. 7)
This leads directly into the next issue, which considers the intensity of a perfection within the sense power. This text indicates the difference between ‘sense organ’ and ‘sense faculty’.