Operation and Actuality in St. Thomas Aquinas's Argument for the Subsistence of the Rational Soul

Abstract

Operation and Actuality in St. Thomas Aquinas's Argument for the Subsistence of the Rational Soul1 Kendall A. Fisher THE HUMAN SOUL is something of an ontological anomaly for St. Thomas Aquinas. It is the substantial form of the human being and so serves as her principle of existence and organization.2 But it is also a subsistent part of the human being—specifically, the part with which she understands. As subsistent, it is not merely the formal principle by which she exists; it exists in its own right, per se, akin, in this respect, to body parts like the hand or eye.3 Yet unlike these body parts, it is a subsistent substantial form, and Aquinas argues that this [End Page 185] ontological status renders it incorruptible. Consequently, it survives death to exist in a disembodied state. Such implications render Aquinas's commitment to the soul's subsistence—and his argument to that end—central to his philosophy of the human person.4 For Aquinas, the soul owes its subsistence to its rational nature. He argues that our intellective acts, unlike sensitive or nutritive ones, cannot be performed by something corporeal, like a bodily organ. Instead, they must be performed by something incorporeal. Aquinas locates these operations in the soul, apart from the body.5 In his view, this renders the soul a per se operator, which in turn entails its subsistence, that is, its existence per se. He holds that "[i] "nothing operates per se unless it exists per se, [ii] for, indeed, nothing operates except a [End Page 186] being in act, [iii] whence a thing operates in the way it exists."6 Since the soul operates per se, it must exist per se. Aquinas's argument rests on the correspondence between a thing's mode of operation and its mode of existence. This is explicit in [i] and [iii]. Yet he does not take this correspondence as primitive. Instead, he justifies it with [ii], nothing operates except a being in act. This requirement that agents be "in act" in order to operate underlies the correspondence between operating and existing per se. Aquinas makes similar moves in other contexts, appealing to variations of [ii] to support correspondence claims regarding operation and existence.7 In fact, [ii] is an instance of a pervasive principle in Aquinas's thought, which frequently appears as "nothing acts except insofar as it is in act" or, "each thing acts insofar as it is in act."8 He employs this principle, which I will call the in-act principle, in myriad contexts. It features in his arguments that God alone creates,9 that all creatures produce their like,10 that incorporeal creatures are incorruptible,11 that the intellective powers are formally in us,12 and others.13 Yet what the principle means and how it serves its justificatory role in the subsistence argument are not immediately clear. Indeed, despite the in-act principle's prominence in Aquinas's thought, it has received relatively little attention in the literature. Perhaps this is because it has sometimes been taken as the truism that agents must exist simpliciter. John [End Page 187] Wippel, for instance, explains the principle by noting that "nonexisting agents do not actually produce effects."14 And, while discussing its role in the subsistence argument, Robert Pasnau explains that what does not exist independently cannot operate independently because "existence is a pre-requisite for operation."15 While true, this reading of the principle is unhelpful for understanding it within the context of Aquinas's subsistence argument. His aim is not simply to establish that the soul exists simpliciter, but to establish that it exists per se and not as a mere formal principle. Other interpreters have taken the principle to be little more than a restatement of one of the correspondence claims regarding mode of operation and mode of existence.16 Norman Kretzmann notes that things that depend on matter (i.e., nonsubsistent forms) cannot act on their own.17 But again, this does little to explain why something nonsubsistent cannot operate per se, and leaves the in-act principle's role in the argument largely obscure. If we can illuminate the...