This chapter turns to Aquinas’s view that the human act is a hylomorphic composite. To discuss the human act’s hylomorphic structure, it first considers three power-exercises crucial to the execution of the human act once the choice has been made, namely, “command,” “use,” and the “commanded act.” It contends that the act of command is an act of reason that specifies the power by which a choice is to be executed. Use is a volitional act that activates, and sustains the exercise, of the power determined by command, and the commanded act is the exercise of this power. It then argues that use (rather than command) functions as the form of the commanded act by virtue of directing the latter to an end. The chapter draws on an insight from Chapter 4, arguing that formal and final causation coincide here, because what it is for a human act to be of a certain kind (and so to have a certain form) is for it to be directed to a certain end. The last section of this chapter discusses Aquinas’s account of how choice explains the hylomorphically organized human act, which relies on the notion of “virtual existence.”

The introductory chapter of this book offers a brief account of the relation between action theory and moral philosophy in Aquinas. It argues that Aquinas has a descriptive, metaphysical account of the human act, one that investigates the human act’s ontology as well as its aetiology, that is, respectively, what the human act is and how it is explained. This account brackets normative considerations about what acts are morally good or bad. The introduction specifies that the book deals with this descriptive theory, and it also motivates the book’s main textual focus, which is on one aspect of Aquinas’s Prima secundae discussion of the human act, namely, the phase leading from choice (electio) to the actual performance of the human act. Finally, the introduction states the main thesis of the book, which is that both choice and the human act that it explains are hylomorphically structured, for Aquinas. Choice is a composite of a volition and a preferential intentional structure inherited from a previous judgment, and the human act is a composite of a volition and a power-exercise caused by volition, such as a bodily movement.

This chapter analyzes the key notion of the “human act” (actus humanus) around which Aquinas’s action theory revolves. It argues that, for Aquinas, the general term ‘act’ is used broadly to denote any power-exercise in nature, whether in the animate or the inanimate domain. Given this broad scope of the term ‘act,’ the chapter considers, in a next step, what sets human acts apart from other power-exercises. It argues that, according to Aquinas, one differentiating feature is that a human act is a hylomophically organized composite of two power-exercises, where a volition that he refers to as “use” is the formal component and a power-exercise caused by volition that he refers to as the “commanded act” is the material component. However, as the chapter also shows, Aquinas chiefly relies on an aetiological criterion to differentiate human acts from other power-exercises, arguing that a human act is explained by a preceding act of free choice. It then shows that choice likewise displays a hylomorphic structure, for Aquinas. It is a volition materially speaking, and its form is the preferential character that this volition inherits from a preceding judgment that Aquinas refers to as the “judgment of choice.”