Epistemological Dispositions Causal Powers and the Human Person

Beginning with the middle sections of the Commentary, the present explicatio considers Aquinas’s remarks on the fifth chapter of Book II of Aristotle’s On the Soul. In Aquinas’s Commentary, this corresponds to Lectio 10, no. 350 and following. The discussions by both Aristotle and Aquinas prior to the mid-parts of book II principally concern the vegetative principles of the soul, which have little direct bearing on sensation and perception and are not part of this inquiry.

The Empedoclean Principle

In the discussions about the principles of intentionality, the concepts of ‘act’ and ‘potency’ occurred frequently. Beginning with Lectio 10 in the Commentary, Aquinas provides an elaborate analysis of these terms, indicating how they are used in various contexts in the philosophy of mind. What emerges, interestingly enough, is the development of a procedure with striking similarities to the ‘family resemblance’ talk common to mid-twentieth century ordinary-language philosophers. Aquinas lists the various ‘uses’ of the concepts of ‘act’ and ‘potency’ in relation to the ‘logic’ of these two concepts. He begins his discussion of act and potency by considering two propositions, which came down to him through various Aristotelian commentators in the long history of philosophy:

• (a) To sense is to be moved or acted upon in some way, for the act of sensation involves a certain alteration of the subject. [. . .]
• (b) It was the view of some inquiries that the passivity of sensation was an instance of ‘like being acted upon by like’. (Commentary on the Soul, no. 350)

These two propositions, rooted in the epistemological principles Aristotle assumed Empedocles to hold, are related to the act/potency distinction because both mention an ‘alteration’ or ‘being acted upon’. Act and potency apply analytically to the Aristotelian notion of change or alteration: ‘Motion is the fulfilment [i.e. act] of what exists potentially, insofar as it exists potentially’ (Physics, bk III, ch. 1). Hence, both concepts of act and potency are central to any discussion of change. Moreover, both of the propositions listed above consider perception as some form of change or alteration.¹