This chapter begins the more speculative part of the book. It responds to two objections to the instrument doctrine. The first objection is that a person cannot use a nature distinct from him as his instrument, even a divine person, because the created nature would lack some necessary feature for it to exist concretely. With the help of John Duns Scotus’s theology of the hypostatic union, the chapter argues that Christ’s humanity can be an instrument of his person because created personality is an extrinsic feature to the constitution of human nature. If Scotus is right, then a divine person can use a really distinct human nature as his instrument without any loss to the fullness of his humanity. The second objection argued that the instrument doctrine amounts to nothing other than the attribution of secondary causality to Christ’s humanity. The chapter argues that the hypostatic union means that the actions of Christ in the flesh are irreducibly distinct from ours, belonging as they do to a divine person.

The argument of this chapter is that the instrument doctrine, if held, sharpens our understanding of other mysteries of the Christian faith, including the hypostatic union, the Church, and the sacrament of the Eucharist. One reason that Aquinas held to the doctrine was the clarity it brought to these other mysteries. With Christology, the benefits are grammatical and speculative. Calling Christ’s humanity an instrument leads us to think of the one who possesses it, namely, the Logos, and so it can render single-subject Christology clearer to the intellect. If Christ’s humanity is held to be an instrument, it also implicates in our understanding the divine power through which the Logos works. With the theology of the Church, the instrument doctrine supports the biblical idea that Christ sends the Holy Spirit on the Church as a human being, and not only as God. And with the theology of the Eucharist, the instrument doctrine assists Catholic faith in perceiving how Jesus gives us a share of the divine life through sacramental communion.

Chapter 1 introduces the instrument doctrine in Aquinas’s thought and explores its foundations in Scripture, focusing on Aquinas’s biblical commentaries. In his commentaries on Romans and 1 Corinthians, among others, Aquinas argues that the logic of scriptural teaching suggests that Christs’ humanity causes divine effects as instrument of the divinity, including our resurrection. The chapter shows how Aquinas interpreted the Scriptures as coherent with the Catholic tradition, especially the conciliar teaching on Christ in the early ecumenical councils. Aquinas thinks that the doctrine should be understood within the conceptual matrix of these early councils’ teaching on Christ.

The introduction states the biblical premise of the book’s argument. In Scripture, God saves human beings through the actions and sufferings of Christ in the flesh. St. Thomas Aquinas developed a theological account of the Incarnation that attempts to account for the way Scripture speaks, namely, that Christ’s humanity is the instrumental cause of salvation, or as the book calls it, "the instrument doctrine." The introduction then gives an overview of the book’s argument: this doctrine best accounts for how Jesus Christ saves Christians in virtue of his humanity. It outlines the argument of the seven following chapters.

This chapter is the heart of the book’s analysis of St. Thomas Aquinas’s teaching on Christ’s humanity as the instrument of the divinity. It explores the various details of Aquinas’s account, outlining it in five synthetic propositions. These propositions, taken together, form the instrument doctrine as St. Thomas conceives of it. Various ambiguities in Aquinas’s account are presented for consideration, and the chapter makes some judgments about how best to understand Aquinas in his mature works. The chapter concludes with a section on the relationship of language to reality in Christology and why reduplicative propositions, used in a standard mode of theological analysis in the thirteenth century, can clarify how to understand the instrument doctrine.

Aquinas recognizes a number of wildly different kinds of individual happiness. What fundamentally unifies these various kinds of happiness so that they all count as varieties of happiness to begin with? This chapter gives a novel answer to this question and thereby identifies a new heart of happiness in Aquinas, which the author calls the Enjoying Good Activities Reading. On that reading, in every case, happiness is exclusively constituted by engaging in and enjoying a genuinely good activity. After giving a brief textual case in favor of reading Aquinas this way, the bulk of this chapter explains Aquinas’s understanding of enjoyment and his account of what it takes for an activity to be genuinely good. This makes clearer what this new reading amounts to and reveals something of its philosophical interest.

The introduction explains the nature of the study, its motivation, its basic structure, and its organization. It draws special attention to the way the book offers a novel interpretation of Aquinas’s account of individual happiness that is remarkably interesting philosophically. It also emphasizes the roles of individual happiness, common happiness, and Holistic Eudaimonism in Aquinas’s efforts to produce a unified ethical system in which law, virtue, and grace also have an important place.

This chapter examines the sort of happiness Aquinas thinks we can have on earth without any special divine help, namely, natural imperfect happiness. After establishing the varieties of natural imperfect happiness Aquinas accepts, it argues that, according to Aquinas, happiness is constituted exclusively by engaging in and enjoying those genuinely good activities that are made possible through the purely natural development of one’s powers. This is the Enjoying Good Activities Reading as applied to ordinary earthly happiness. The chapter then explains the various roles that everyday goods play in happiness so understood. Because of the role those goods play, it turns out that this sort of happiness is somewhat fragile. After giving an account of just how fragile it is, the chapter ends by considering Aquinas’s understanding of degrees of natural imperfect happiness.

Because the full reconstruction emerges piecemeal over the course of the study, this chapter starts by summarizing the most fundamental ways in which Aquinas connects the big-picture elements of his ethics through his understanding of happiness, both individual and common. The chapter then offers reasons for thinking that Aquinas’s ethics of happiness is still worth taking seriously today. In particular, it focuses on three illustrative aspects that make Aquinas’s ethical views distinctive and appealing. The first is Aquinas’s account of the nature of happiness and how that account fits into his broader understanding of well-being. The second is Aquinas’s account of the relationship between the right and the good. The third is Aquinas’s account of the most comprehensive role that virtue plays in ethics and human life.

Aquinas recognizes a number of wildly different kinds of individual happiness. What fundamentally unifies these various kinds of happiness so that they all count as varieties of happiness to begin with? This chapter starts to answer this question and thereby starts to home in on the true heart of happiness in Aquinas. Because perfectionism was predominant in Aquinas’s time, the chapter starts by laying out three importantly different varieties of perfectionism about happiness. It turns out that different commentators have treated each of those three varieties of perfectionism as the version that Aquinas endorses. So this chapter predominately explains and evaluates each of these three readings of Aquinas, while also drawing out lessons to be incorporated into any adequate novel account of the heart of happiness in Aquinas.

This chapter examines the sort of happiness Aquinas thinks we can have on earth with the help of God’s grace, namely, graced imperfect happiness. In keeping with the Enjoying Good Activities Reading, it argues that, according to Aquinas, happiness is constituted exclusively by engaging in and enjoying some suboptimal genuinely good activity, animated by God’s grace. After introducing Aquinas’s understanding of grace, the chapter works through Aquinas’s reflections on the Fruit of the Holy Spirit and the Beatitudes. From those reflections, it becomes clear both how Aquinas thinks about graced imperfect happiness generally and how he thinks about its basic varieties. The chapter closes by reflecting on graced imperfect happiness’s place between the perfect happiness of heaven and the natural imperfect happiness of those on earth living apart from God’s grace.

This chapter explains the many ways in which individual happiness and common happiness are related to Aquinas’s account of virtue. It begins by arguing that virtue is strictly necessary in order for an individual to be happy, but still virtue is not a constitutive part of that happiness. Rather, it is strictly necessary because virtue alone enables the individual to engage in and enjoy genuinely good activities. The chapter then argues that, still, according to Aquinas, virtue is more deeply related to common happiness than individual happiness inasmuch as a character trait is a virtue of character fundamentally because it enables a person to play their part in realizing the common happiness of their community, not their own individual happiness. The chapter thereby establishes the third element of Aquinas’s Holistic Eudaimonism. The remainder of the chapter shows how the master virtues of general justice and charity as well as a whole host of other particular virtues concern aiming at and securing common happiness for the community.

This chapter explains the many ways in which individual happiness and common happiness are related to Aquinas’s account of law, both generally and with respect to some particular laws. The chapter begins by arguing that, by its very nature, every genuine law orders the things under it to the common happiness of some community or other. It then argues that, according to Aquinas, moral laws order us to common happiness by outlining universal and absolute rules that must be followed in order to fully realize common happiness. Unlike many have thought, then, Aquinas holds that our moral obligations are fundamentally determined by facts about which norms must be followed in order to realize common happiness, not individual happiness. That is the second element of his Holistic Eudaimonism. On the other hand, when it comes to civil laws, the chapter argues that Aquinas advocates a kind of top-down, restricted rule-consequentialism with common happiness as its goal.

This chapter starts by arguing that, for Aquinas, common happiness is a fundamental and crucial notion, despite the fact that he very seldom discusses it and it has largely been ignored by commentators. It then sets out Aquinas’s understanding of the nature of common happiness with special attention to two models of common happiness, namely, the community of heaven and true friendship. The chapter then argues for the perhaps unprecedented claim that Aquinas is committed to the idea that common happiness is the true ultimate end of each human being. It thereby establishes the first element of Aquinas’s Holistic Eudaimonism.

This chapter argues for a fairly radical rethinking of Aquinas’s account of perfect happiness. In particular, it argues that, according to Aquinas, perfect happiness just is the fruitio of God, understood as a complex activity involving both the vision of God and maximal enjoyment of God. This fits very well with the Enjoying Good Activities Reading laid out in Chapter 2, since perfect happiness so understood clearly involves engaging in and enjoying a genuinely good activity. From there, the chapter explains what makes that perfect happiness so special, in part by comparing that happiness to God’s own happiness. After explaining the relationship between the fruitio of God and other heavenly goods, the chapter closes by showing how Aquinas makes sense of the idea that perfect happiness comes in degrees and how it is that resurrected bodies and other people are supposed to make us happier in heaven.