This admirably clear book will be of interest and value primarily both to scholars of Augustine, and scholars of the later history of thought on the relationship of grace to human freedom and moral decision-making. As the title suggests, it carefully explores how Augustine drew upon, synthesized, and developed largely Stoic and Platonic theories of perception and judgement. The book starts with Augustine's famous account of his conversion at Milan in Book Eight of the Confessions, but ranges over a wide range of texts and makes good use of Augustine's sermons to test proposed interpretations of specific terms. A picture emerges of Augustine's initial and lasting debt to earlier philosophers, but also of three phases of development in Augustine's thinking as he struggled to integrate his account of moral decision-making with his understanding of God's omnipotent grace: between 394 and 400 (a period already much studied by others); between 411 and 421; and a third period from 426 onwards.

Chapter One introduces us to Stoic epistemology, and the notion that all human perception carries with it a linguistic dimension: even a first impression strikes us in at least one of several ways that have a specific linguistic form. Every impression we receive, even a false impression, includes the assertion that it is what we think it is, but there may be other types of ‘sayable’ thoughts as well: several sorts of question, imperatives, assertions, and exclamations (p. 9). It is then for the person who has received the impression to respond, to withhold or give assent, for example, to the assertion it contains, and to any imperative, after due consideration. At this second stage a person is morally obligated to act wisely and not rashly (p. 15). Sarah Byers concludes the chapter by showing how Augustine accepts this basic epistemology. Chapter Two looks specifically at motivation, and at the Stoic doctrine that ‘emotions are caused by perceptions that something good or bad has been, or will be, lost or gained’ (p. 23). A motivating impression will then be one that contains an imperative. Byers again shows how Augustine accepts this theory and she proposes that in Augustine's writings a ‘suggestio’ is exactly what in Stoic terms would be a motivating impression (pp. 30–32). From here, Byers looks at Augustine's account in the Confessions of his own moral indecision when invited to embrace celibacy. It is presented not as a conflict between reason and the lower passions or appetites, but as a conflict between contradictory impressions, where this involves competing thoughts (pp. 39–24). The second half of chapter examines how Augustine integrates this Stoic scheme with a Platonic account of action which is prompted by love of what is noble. Where Stoic theory gives us the mechanics of how we come to do what we do (our thought processes), the Platonic account tells us why we act in this way, what we intend in so acting (p. 47).

The next four chapters, Three to Six, look at the affective life, and show both a more critical and a creative side to Augustine's engagement with the Stoics. Byers begins with his debt to their teaching that ‘emotions are caused by beliefs about events, rather than directly by events ’ (p. 58). Where the City of God stresses Augustine's disagreements with Stoicism (in his recognition of external and bodily goods, and in the value he places on compassion), analysis of other texts shows how far Augustine agreed with Stoics; for example, on the moral blame which attaches to passions that result from false beliefs (pp.60–68). Even where Augustine disagrees with the Stoics in allowing for a virtuous sorrow occasioned by a wider range of losses, this range will not occasion deep or prolonged grief. Chapters Four and Five concern not full-blown emotions, but the affective states that precede them: what Stoics termed propatheia or ‘preliminary passions’, and the equivalent early stages of virtuous emotions. Byers argues that in his sermons Augustine improved on the Stoic theory of propatheia ‘by identifying the cause of preliminary passions as doubt, meaning a dubitative sayable subsisting in an impression’ (p. 101), while the bishop has far more to say than Stoics about the preliminary affections that could blossom into virtuous emotions, especially the joy that Augustine holds to be characteristic of the Christian life (p. 128). Chapter Six looks at the pastoral implication of all this: the ‘cognitive therapy’ Augustine advocated to prevent preliminary passions from turning into vicious emotions.

Chapter Seven finally relates Augustine's theory of the emotions and moral decision-making to his changing understanding of grace, and compares Augustine's several accounts with those later offered by Báñez and Molina. The topic arises out a problem concerning the cognitive therapy Augustine adapted from the Stoics: what will sufficiently motivate someone in need of such therapy to undertake it? Augustine accepted the philosophical commonplace in Late Antiquity that the vicious person is blind to his or her own moral good (pp. 172–73). In his view, original sin means that we are all born with this moral blindness, and as Adam's offspring we carry the blame for it (p. 177). Only grace can spring us from this trap. As Byers summarizes: ‘grace is God's action on the mind, whereby the intellect apprehends the beauty and goodness of virtue, and as a result formulates sayables including an imperative, in the discursive reason. This is the motivating impression’ (p. 182). Conversion comes either directly as a result of this impression or after a second grace whereby the mind is moved to consent to the earlier graced impression. The last twenty-five or so pages of the chapter look at how Molina and Báñez each drew on different aspects of Augustine's position, though neither faithfully reproduced it. Molina's insistence that ‘free choice is always able to do otherwise’ (p. 195) is shown to be alien to at least some of what Augustine says about grace, while Báñez pays insufficient attention to those places where Augustine allows for a human response to a graced motivating impression before God gives a second grace of consent. For Byers, the story is then complicated by Augustine's later moving away from this ‘dialogue’ model of conversion, in which there is space for both divine initiative and human co-operation, to a model after 425 of concurrent grace operative through human decision-making, where such grace is necessarily irresistible, both because of its strength as the grace of Christ, and because of God's omnipotence as Creator. This latter position Byers believes to be flawed, and it is here that Thomists may take issue with her all too brief analysis of the philosophical problems. Nonetheless, this is an excellent book which makes a very helpful contribution to our understanding of Augustine both as a philosophical theologian and as a scripturally trained contributor to the philosophy of the emotions.