Action, Supposit, and Subject: Interpreting Actiones Sunt Suppositorum

The claim that "actions are of supposits" appears numerous times, in this and other formulations, in the writings of St. Thomas Aquinas.¹ Interpreters of Aquinas cite this thesis in discussions of Aquinas's cognitive theory, his account of personal identity (including in the recent dispute between survivalism and corruptionism), and his Christology.² Alain de Libera, in his work tracing the historical development of the modern subject, has proposed that Aquinas's use of this thesis helps to pave the way for the emergence of the "subject-agent," the self that is the subject of all cognitive activity.³ There is a tendency in the recent literature that cites this thesis to take its meaning for granted: recent readers of Aquinas such as Carlos Bazán, Jean-Baptiste Brenet, and Corey Barnes all take this thesis to mean that the supposit—the individual existent, the primary substance, or the person (where applicable)—is the subject of actions.⁴ De Libera himself offers "actions belong to subjects" as a translation of actiones sunt suppositorum, and he calls this thesis the "subjective principle of action."⁵ There is a uniform tendency, in recent literature on Aquinas, to transition quickly from the term "supposit" (or "person") to the term "subject," without fanfare.⁶

According to its typical meaning in Aquinas's usage, the term "subject" (subiectum) picks out something that stands, in relation to that of which it is the subject, as potency to act.⁷ In this sense, a subject is something that is actualized, as by a formal principle. Given this, if we interpret "action is of the supposit" to mean that "the supposit is the subject of action," without fanfare, we can wander into interpretive difficulties. Aquinas holds that human intellectual activity is an operation that occurs through the soul itself rather than through any part of the living body. Although the operations of sensation and of vegetative life occur in and through bodily organs—parts of the living composite of body and soul—Aquinas insists that the intellectual power and its operation are in the soul alone "as in their subject."⁸ This might seem to contradict any claim that the human person, who is the composite of soul and body, is the subject of intellectual activity as an action. Recent interpreters of Aquinas reach seemingly contradictory conclusions about whether the human soul or the human person should be characterized as the subject of intellectual activity.⁹

In addition to its purely anthropological application, whereby Aquinas claims that actions that are proper to the soul are nevertheless the actions of the human person, Aquinas also employs the thesis actiones sunt suppositorum in his discussions of the actions of Christ, the divine person who subsists in two natures. It is the divine Word who, according to his human nature, senses, understands, weeps, and suffers. Here too, the quick transition from the term "supposit" (or "person") to the term "subject" may lead to philosophical difficulties. For if we identify the divine Word as the subject of his human action, does this mean that we are positing within the divine Word a potency that is actualized? Although this aspect of the question will not be my focus in this piece, the interpretation of actiones sunt suppositorum has major implications for Christology.

The purpose of this brief study is threefold: (1) to clarify the meanings of the term "subject" in Aquinas's thought; (2) to examine in what senses the human soul and the human person should be characterized as subjects of intellectual activity; and (3) to show that actiones sunt suppositorum is consistent with the view that the human soul operates per se and is the sole "actualized-subject" of its per se operation. I will argue that, for Aquinas, the truth of actiones sunt suppositorum is founded upon the metaphysical unity of the person rather than upon a claim, foreign to Aquinas's thought, that the person is the proximate actualized-subject of human action. At the very least, I will show that speaking of the human person as "the...