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.

Chapter 9 offers a concluding summary of the major topics and themes in the work. The chapter opens by noting that the book aims at recovering the philosophical background in Aquinas needed to understand the Five Ways. The chapter then offers a summary of each of the previous eight chapters. There is a brief discussion of how the Ways build on each other to suggest a composite view of the divine nature as creator and governor of all. A closing section of the chapter offers a few closing thoughts. Those interested in philosophical arguments for God are rewarded by careful study of the Five Ways. Reading Aquinas often challenges our own philosophical views. The richness and complexity of Aquinas’s thought benefits our own thinking through the great problems of philosophy and theology.

Chapter 1 has three main topics: the structure and aims of the Summa theologiae, faith and reason, and the type of demonstration Aquinas uses in the Five Ways. First, there is a look at the divisions of the Summa into (three) Parts, Treatises, Questions, and Articles. The articles are structured like a debate. The work’s Prologue suggests that Aquinas writes for students of theology but he well knows that his experienced peers in the Church and universities are interested in his theological positions. The chapter then treats his views on faith and reason, mainly in Summa theologiae Ia q.1. It looks at the nature of “sacred teaching” (sacra doctrina). A central theme is how Aquinas sees the legitimate findings of human reason as compatible with revelation, rightly interpreted. Finally, the chapter explains how Aquinas settles on a certain method of demonstrating God’s existence, called a demonstration “quia” or “that” God exists.

Chapter 5 examines the Second Way, which starts from observing an ordering of efficient causes in the world and concludes to a first uncaused cause, which is God. After giving the translation and premises of the Second Way, I briefly compare the First and Second Ways and then look at what efficient causation involves for Aquinas. The rest of this short chapter considers the Big Bang as a rival account of the origin of the universe to invoking a divine nature. The chapter closes by briefly considering a multiverse.

Chapter 8 examines the Fifth Way, which argues for God’s existence from natural bodies acting for an end or purpose. After a translation and the premises are given, the chapter explains how the Fifth Way works and its relevant differences from William Paley’s argument from design. There is a look at teleological arguments for God in Aquinas’s other writings. The chapter examines in what sense(s) Aquinas thinks that natural bodies act for an end and also for a certain good. There is a look at his arguments for final causes in nature. Attention is given to why he holds the crucial premise that bodies which lack intelligence, but act for an end, are directed to their end by something with intelligence and understanding of that end. There is a brief discussion of chance, which Aquinas sees as a rival explanation to finality in nature. The chapter closes with the final steps of the Fifth Way where Aquinas appears to see a single guiding intelligent being in the background of nature.

Chapter 7 examines the Fourth Way, which argues from the gradations of being, truth, goodness, and other perfections found in things, to a first cause utmost in being and perfection. After a translation and the premises are given, the chapter explains what assigning a gradation of these terms involves for Aquinas. There is discussion of a key implication of the Five Ways that God is “subsistent being itself,” that God’s essence is God’s existence. Next, there is a discussion of the premise that there is a maximum in every genus which is the cause of all other things in that genus. Thus, there is a maximum in being, truth, and goodness which causes these in all other things. This is God. A closing section discusses the doctrine of continuous creation in Aquinas, that God sustains all else in existence at every moment. There is a look at the contemporary debate over the need for a God to do this, which is termed divine conservation versus existential inertia.

The Introduction states the book’s main purposes in examining Thomas Aquinas’s (1225–1274) famous five arguments for God’s existence, or “Five Ways,” in Summa theologiae Ia q.2 a.3. Even philosophically trained readers find them difficult to understand and often misread them. There are few extensive books in English solely on the Five Ways in the last few decades. Reading the Ways requires familiarity with positions Aquinas holds in his metaphysics, theory of causation, logic, semantics, theory of knowledge, philosophy of nature, and other areas of philosophy. This book recovers that necessary background for the reader. Careful attention is given the arguments’ premises and the reasoning behind them. Ample consideration is given to historical and contemporary objections to the various Ways and how Aquinas might respond. The Introduction closes with a summary of the book’s nine chapters. It is hoped that readers will think along with Aquinas on issues surrounding God’s existence and reach greater clarity in their own conclusions.

Aquinas holds a version of the causal principle, that things which cannot of their essence fully account for their existence require an outside cause to exist. Chapter 3 goes further into Aquinas’s views on causation and issues surrounding accounting for why things exist. The discussion uses as a point of departure the classic question, “Why is there something rather than nothing?” The chapter looks at various approaches to, and critiques of, the question. This includes the views of Leibniz and also those of Bertrand Russell and Fredrick Copleston in their famous radio debate in 1948 on the existence of God. There is then a look at David Hume’s serious challenge to the view that whatever begins to exist must have a cause. The chapter then turns to how quantum scientific developments in the twentieth century are seen to pose problems for the causal principle. Might quantum considerations offer a universe from nothing? A last section looks at whether there are philosophical considerations positively supporting the causal principle.

Chapter 2 covers elements in Aquinas’s metaphysics and his views on causation as part of the philosophical background for understanding the Five Ways. Attention is given to Aristotle’s explanations of change and his four causes: material, formal, efficient, and final. The chapter then examines Aquinas’s metaphysics of existence and his distinction between essence and existence, which features a contrast between caused and uncaused existence prominent in the Five Ways. There is a brief look at some more recent views of existence influenced by Immanuel Kant and others, which call Aquinas’s views into question. Finally, the chapter explains Aquinas’s model of explanation, that is, his views on what needs accounting for and how it is to be done. (There is some contrast with Gottfried Wilhelm Leibniz’s views.) Aquinas seeks a complete account for why contingently existing individual objects exist at all and undergo changes. He thinks that what has caused existence must ultimately be accounted for by what has uncaused existence.