Nicholas Austin's important study offers a broad and comprehensive exposition of the virtue theory of Thomas Aquinas. But more than mere exposition, Austin offers an interpretive analysis of Aquinas’ approach to virtue by examining this topic through the lens of Aristotle's theory of causality, which Aquinas and his contemporaries adopted as their own. This causal approach offers distinctive insights into Aquinas’ virtue theory and also links Thomas’ reflections on the moral life to his most foundational metaphysical and theological commitments, a connection that is too frequently minimized.

After an opening chapter that displays, in anticipatory fashion, the explanatory power of this causal approach by analyzing the virtue of temperance in terms of its causes, Austin devotes three chapters to a careful examination of the definition of virtue that Aquinas develops in the Summa theologiae. After treating Aquinas’ rather Aristotelian approach to defining virtue as a good, operative habit, Austin pauses to consider why, in the final article of the question, Aquinas opts to defend a different definition, which is of Augustinian provenance, although mediated most proximately through the Sentences of Peter Lombard. This move has long been a source of debate among Thomists who disagree about whether Aquinas’ understanding of virtue is best characterized as Aristotelian or Augustinian. Austin, however, astutely observes that Aquinas’ defense of the Augustinian definition of virtue stems not from the definition's indebtedness to Augustine but rather from the fact that it defines virtue comprehensively, which is to say in terms of its causes.

In the book's remaining chapters, Austin unpacks Aquinas’ causal definition of virtue by attending to seven causal elements of virtue in general. These seven aspects are derived from and associated with the traditional four causes (formal, material, efficient, and final) of Aristotelian metaphysics. In terms of material cause, Austin examines a virtue's subject, which is the particular capacity or power of the human person that a virtue perfects, and the matter, which refers to the specific domain of human life in which a virtue enables the human person to pursue the good. With respect to formal causality, he considers the mode (which he sometimes calls the formal object), which is a virtue's characteristic manner of achieving the good in its particular domain, as well as the virtue's exemplar, which refers to the ontological ideal of that virtue as it exists in God. With respect to final causality, he considers both the target, which is the proximate good that a virtue pursues, and the end, which is the more comprehensive conception of human flourishing to which the virtue is ultimately directed. Finally, in terms of efficient causality, Austin examines the agent, which is the means by which the virtue is generated and increased.

Throughout his exploration of the causal model of defining and describing virtue, Austin manages both to identify the major contours of Aquinas’ thought and also to apprise readers of contemporary questions in Thomistic virtue ethics. For example, Austin wades into the dispute among Thomists over whether the acquired and infused moral virtues can coexist in the same subject, and he explores the Thomistic debate about how virtue brings the passions of the soul into conformity with reason. Austin's exposition of these debates also prompts him to propose new solutions, which emerge from his causal reading of Aquinas’ virtue theory. These novel proposals further demonstrate the potential fruitfulness of this hermeneutical approach. In addition to touching on intra-Thomistic debates, Austin's interests also bring him into conversation with broader questions in virtue ethics, such as the challenge of situationism and debates about whether virtues can be misused.

This book has the potential to appeal to a broad audience. Its novel interpretation of Thomistic virtue theory and robust engagement with a variety of interlocutors—including contemporary Thomists, philosophical virtue ethicists, and (perhaps most uniquely) the tradition of medieval and early modern Thomistic commentators—will make it of particular interest to scholars of Aquinas. At the same time, its accessible prose and inclusion of suggested readings from Aquinas’ texts also makes it suitable for classroom use with advanced undergraduates or graduate students. Austin has done proponents of virtue ethics a great service by providing a clear, concise, and contemporary guide to Aquinas’ virtue theory.