St Augustine's doctrine of the Trinity has been the subject of much criticism over the past century. Lewis Ayres’ Augustine and the Trinity aims to contribute to the rehabilitation of the great Latin doctor on points of both doctrine and method.

If the book has a dominant point of view, it is that Augustine's theology should be understood chiefly as an expression of Latin pro-Nicene tradition. Ayres points, then, to the ways in which Augustine made use of the wider Latin liberal arts tradition, and more specifically how his use of philosophy was a rather piecemeal enterprise which gradually unfolded during the course of his career. Augustine's work on the Trinity likewise developed considerably over time, and it was often experimental, including the great De Trinitate itself.

To my mind the most important part of the book is Ayres’ analysis of De Trinitate books 5–7, where Augustine takes up the logic and terminology of trinitarian doctrine in ways which have had a profound impact on subsequent Western theology. Ayres expertly shows that in these books Augustine is not so much concerned with ontology as he is with questions of predication which arise from the biblical text. This non-technical, exegetical approach is reflective of earlier Latin anti-monarchian traditions, as is what Ayres regards as Augustine's clear intent to uphold the traditional doctrine of the monarchy of God the Father – the view that the Father is the unique source of the Trinity. On this last point, I would suggest that Augustine's anti-monarchianism is characteristic of certain passages as opposed to others, and that the two sorts of argumentation do not always fit together as neatly as Ayres supposes; nevertheless, Ayres’ elucidation of these themes has far-reaching consequences for the study of Augustine's trinitarian doctrine.

The book's defining polemic is to oppose the interpretation of Olivier du Roy who, in a brilliant slip, is named ‘Theodore’ in the index, Theodore de Régnon being the other great nemesis of current pro-Augustinians. Ayres refutes Du Roy's influential claims that in Augustine's work the incarnation merely serves as extra assistance for those too weak to ascend to God by reason alone, and that such an ascent is a participation in the trinitarian structure of reality based on Plotinian hypostases. To be sure, the incarnate Christ plays a central role in Augustine's work; Augustine's critique of philosophy from Confessions to City of God is much sharper and deeper than many have cared to notice; and his understanding of the relationship between the Trinity and the psychological structures explored in De Trinitate books 9–14 is nearly the opposite of what Du Roy believes it is – so far so good. Then we come to Du Roy's final claim, that Augustine produced a monistic view of God in which the distinctions among the three divine persons are relatively ignored, with support from Augustine's theory of appropriations. Here Ayres’ response is less than convincing (pp. 227–9 and chapter 10). In short, to say that Augustine's handling of trinitarian appropriations is a ‘logical deduction from scriptural language’ and ‘a mode of teaching employed by Scripture’ begs the question in significant ways. Even though, in certain texts, Augustine discusses the Son's role in the divine economy and his identity within the Trinity in ways which are more akin to the Cappadocians and Hilary of Poitiers, it does not follow that such arguments mitigate others which do show the monistic tendency which De Régnon and Du Roy have identified. Augustine's exegetical choices in the latter passages often run counter to the plain(er) sense of the biblical text and the exegesis of most other fourth- and fifth-century pro-Nicene theologians, who consistently stress the distinctive, eternal propria of each of the three persons, and such arguments are not explained away simply by aligning Augustine with earlier Latin anti-monarchianism.

This is an important book, but it is not for the faint of heart. Ayres’ prose is dense and at times abrupt, and the overall discussion is thickly embedded in the scholarly debates of the last century. Yet that will also be its lasting strength; for Ayres has succeeded in bringing a vast amount of painstaking research and helpful new perspectives to the study of Augustine's trinitarian theology. Augustine on the Trinity will be of keen interest to any theologian or advanced scholar who seeks guidance in navigating the vast sea of Augustine's theology.