Aquinas thinks that natural efficient causes can act through the active powers of substances distinct from themselves. Aquinas identifies two ways in which an efficient cause can operate through another cause’s power, namely as an instrumental cause or as a secondary cause. The chapter discusses Aquinas’s basic understanding of instrumental causality and secondary causality. Instrumental causes are employed by another cause, called a principal cause, to reach its end. In acting for a higher end, the instrument acts through the principal cause’s power. Secondary causes are like instruments insofar as they cannot act unless a higher cause exercises its power. However, secondary causes differ from instruments insofar as they act for their own ends. The chapter discusses Aquinas’s examples of instrumental and secondary causality in the natural world. Aquinas uses of the notion of instrumental causality to understand how higher-level natural powers, such as the nutritive power, employ the actions of elemental powers, such as heat, to reach their ends. He regards terrestrial causes as secondary causes that act through the power of the heavenly bodies.

Virtues are capacities by which agents are able to produce good acts consistently, pleasurably, and for their own sake. This book presents Thomas Aquinas’s more general account of virtue in its historical, chronological, philosophical, and theological contexts.

Chapter 2 is on the distinction between intellectual and moral virtue, which was first clearly delineated by Aristotle. Moral virtues correspond to what are most commonly recognized to be virtues, such as justice and courage. Intellectual virtues are habits of knowing that do not on their own make the agent good. Prudence, however, is significant as an intellectual virtue precisely because of its connection with the moral virtues. Prudence depends on moral virtue, and each moral virtue depends on prudence. Thomas emphasizes that the one virtue of prudence covers the material that belongs to all of the distinct moral virtues.

Chapter 6, which is the last chapter, considers the importance and contemporary relevance of Thomas’s understanding of the virtues in light of what has been established in the previous chapters. The virtues are not basic to Thomas’s understanding of moral goodness in the way that they are in some contemporary versions of virtue ethics. Nevertheless, they are needed to organize and account for the various ways of living a full life. Contemporary sciences might add precision or material to Thomas’s account, but it is not clear that they require radical changes to it.

Virtues are capacities by which agents are able to produce good acts consistently, pleasurably, and for their own sake. This book presents Thomas Aquinas’s more general account of virtue in its historical, chronological, philosophical, and theological contexts.

Chapter 3 considers the various divisions of moral virtue. This chapter describes Thomas’s response to the Stoic thesis that the virtuous person lacks passions. Aristotle states that some moral virtues are about the passions. The chapter ends with a discussion of the Neoplatonic thesis that there are different kinds or stages of virtue that lead to contemplation.

Chapter 1 considers Thomas’s definition of virtue as a good operative habit. To understand this definition, we must first consider how “habit” is a philosophical term that has no counterpart in ordinary English. Moreover, Thomas explains and defends this definition in light of the various authoritative definitions that are available to him, including especially definitions from Aristotle and Peter Lombard.

Chapter 5 is about the properties of virtue. These properties follow upon a virtue by the simple fact that it is a virtue. There are four such properties that seem rather loosely connected: the mean of virtue, the connection between the virtues, the order of the virtues, and the duration of virtue after this life. Despite this somewhat loose ordering, each of these properties must be studied if we are to understand Thomas’s account of virtue as a whole.

Chapter 4 is about the distinction between natural and supernatural virtue. Natural virtues are acquired through human effort and are studied by philosophical ethics. Supernatural virtues must directly come from God. Their existence is known only through revelation. Thomas’s predecessors and most subsequent theologians typically identified these infused or supernatural virtues with the three theological virtues of faith, hope, and charity. Theological virtues are directly about God. But Thomas thinks that there must also be distinct infused moral virtues that exist alongside the acquired moral virtues. These infused virtues are specifically distinct from the acquired moral virtues that share the same matter and from the theological virtues that are about God.