Weigel’s Reading Aquinas’s Five Ways joins a small group of well written introductions to arguments for God’s existence written in the last decade. Among these are Edward Feser’s Five Proofs of the Existence of God, which, while sounding from its title like an extended treatment of the quinque viæ of the Summa Theologiæ, in fact departs from St Thomas’s approach and synthesises arguments from ancient, medieval and modern sources to produce five arguments that Feser feels to be the strongest. Another, Gaven Kerr’s Aquinas’s Way to God, offers what he feels to be the Thomistic argument for God’s existence taken from the distinction of essence and existence in De Ente et Essentia, IV. So, among these clear and concise introductions for God’s existence, Weigel’s work is rare a rare example of an introductory exposition of the Ways marked out by St Thomas in Question 2, Article 3, of the Prima Pars.

But that its focus is explicitly on the Summa Theologiæ, and offers a faithful exposition of St Thomas’s thought, Weigel’s work is expansive. While many introductions to the Summa Theologiæ, or to particular parts of St Thomas’s thought might focus rather narrowly, Weigel is keen that readers should understand Aquinas’s proofs within a greater picture, both within the Summa itself, and within the wider body of Thomas’s works.

In his consideration of the wider terrain of the Summa Theolgiæ, Weigel stresses that the viæ of Prima Pars Question 2, Article 3 stand between Question 1 on Sacra Doctrina, and a larger body of questions in the Summa Theologiæ on God’s Simplicity, Perfection, Goodness, Immutability, Eternity, and Unity. In other words these viæ are not St Thomas’s last words on God’s existence, or indeed his completed work of proving God’s existence. To get a clearer idea of what St Thomas is trying to achieve in Question 2, Article 3, we must read further on in the Prima Pars and indeed not just the treatise De Deo Uno. One example of this will have to suffice here. In his consideration of the Fifth Way—the argument based on the governance of creation—Weigel draws our attention to the fullest context of the Prima Pars, showing us how different questions coinhere around particular topics. So, providence is dealt with explicitly in Questions 22, 103, and 104 of the Prima Pars, but also stands behind the Fifth Way in Question 2. Again, the unity of God is argued to in Question 11 in part on the basis that ‘…things that are diverse do not harmonise in the same order, unless they are ordered thereto by one’ (ST Ia, 11, 3, resp.). In other words, the order of a diverse creation points to the unity of God. Questions of providence also stand behind Aquinas’s affirmation of the goodness of creation where Aquinas argues that creation’s diversity works for the end of all things in God, and, indeed, in its intricate profusion, unified towards a single end, sings of God’s goodness (ST Ia, 65, 2, resp.).

Within the wider body of St Thomas’s work, Weigel very clearly draws out other arguments that are made by St Thomas for God’s existence, which differ to a greater or lesser extent from those offered in the Five Ways in the Summa Theologiæ. Again, using the example of the Fifth Way, we find a similar argument made in the Summa contra Gentiles Book I, Chapter 13 and De Veritate Question 5, Article 2. Here it is worth noting a little frustration I had. Weigel very deftly explains the difference in the arguments made but offers little explanation of why these arguments were made differently, and in these moments the reader is left slightly hanging. Of course, to fully explain these differences would have been to write a different kind of book, no longer an introduction to the Five Ways in the Summa but rather a much more specialised book on the broader context of St Thomas’s body of work. Still, a little more contextualisation would have been helpful in these moments.

Any frustrations on this account are, however, more than made up for by Weigel’s synthesis of the secondary literature. Even where one feels a little more explanation could have been helpful, a footnote directs you to a range of secondary literature for greater focus. Moreover, different interpretations of the various ambiguities of language found in the various Ways is clearly laid out to aid navigation of the interpretative terrain. In this respect, Weigel offers a text book introduction from which the neophyte philosophy student and the experienced academic can profit. Authors of other introductory volumes would do well to learn from Weigel’s example of clear synthesis and footnotes that are detailed but not laboured.

Weigel’s exposition of the Five Ways is rich most of all because it does not simply rest in an exposition of the Summa Theologiæ. We are taken through St Thomas’s work, from Aristotelian commentaries to disputed questions, from the Summa contra Gentiles to the Summa Theologiæ, and this in itself is something of an education not just in St Thomas but in the Ways themselves. In a celebrated, although perhaps rather obscure exposition of the word via in Dominican Studies in 1954, R. A. Markus traces the meaning of the word ‘way’ across the corpus of St Thomas’s work, with a particular focus on Thomas’s reception of the three ways of Pseudo-Dionysius and their integration in his Commentary on the Sentences and his two Summæ. The proofs that we arrive at in the Summa Theologiæ are, along with all the others offered by St Thomas, a peculiar kind of proof that really offer us a journey, or an itinerary for a journey. These itineraries are, Markus argues, much more concrete than arguments; they are, instead, itineraries that help us to put the world around us to the question, to use Markus’s rather striking turn of phrase. These viæ, ways, itineraries, proofs, arguments can be a little impenetrable for both neophyte and expert alike, and with Weigel’s clear and detailed introduction, we have help in opening up the richness of St Thomas’s body of work and, more importantly, help in opening up the richness of the created order according to the mind of St Thomas.