As the author explains at the start of this hefty study, much ink has been expended over the last half century in elucidating Augustine's account of the human will, in assessing its development and cogency, and in assessing its originality or indebtedness to earlier writers, in particular to the Stoic philosophers. Since Albrecht Dihle's 1981 book The Theory of the Will in Classical Antiquity, scholars including Anthony Kenny, Carol Harrison, Richard Sorabji, John Rist, Michael Frede, and Sarah Catherine Byers have each reached different conclusions. The task is complicated by lack of certainty as to when Augustine wrote certain texts and by the nature of many texts as polemical contributions to theological disputes in which different aspects of the will are germane to the argument. This makes it difficult to know when what is written in one place may guide interpretation of what is written elsewhere. Han-Luen Kantzer Komline addresses the subject through a painstaking analysis of the textual evidence that is careful not to attribute to Augustine at one time or in one text what he says elsewhere at another. Across eight chapters, framed by an introduction and conclusion she builds up a persuasive if scarcely surprising account of how Augustine describes the human will and the role which such descriptions play in his theological controversies. Each chapter takes a different theme but ‘also finds its centre of gravity in a certain period of Augustine's thinking, with successive chapters moving forward chronologically’ (p. 8).

The picture which emerges across the first two chapters is of an early period after his abandonment of Manichaeism, in which Augustine views our possession of a free will as self-evident and asserts that ‘there is nothing so much in our power as the will itself’ (De libero arbitrio, Book 3). However, after his engagement with the Pauline scriptures as a newly ordained presbyter, this gradually gives way to a ‘theologically differentiated’ account of the will, as originally created, as fallen, as redeemed in this present age, and as it will be in the life to come. Already by 392, in the Contra Fortunatum, Augustine contrasts Adam's freedom of the will before the Fall with his fallen state when he sins through necessity, which is the pattern Augustine thinks observable in the lives of all Adam's descendants. He also contrasts the grip of sinful habits with a new freedom granted by divine grace (pp. 84–5). Book 3 of De libero arbitrio limits free will to Adam before the Fall (p. 87). Augustine's understanding grows more complex in the course of writing the Ad Simplicianum after ordination as a bishop which brought further study of St Paul. Here, Augustine argues that a person without grace may know what is right, and wish she or he could do what is right, but still does what is wrong. Sin is not so much a ‘problem in the will's orientation but … a matter of the will's bondage or weakness’ (p. 91). Augustine now reaches the fundamental insight that God's grace is not given on the basis of some prior merit but is creative of a good will. To come to faith, God must inspire delight in God's goodness and offer of salvation. Nor can such a grace be resisted (p.104).

In Chapter Three the author examines how Augustine's understanding of a good will ‘evolved’ over many years ‘in the context of the Pelagian controversy’) and in particular his view of what such a will can actually do (pp. 123–4). Across three stages (A.D. 411–17, 417–21, and 421–430) Augustine moves from a sense that faith is in our power to accept or reject, if first graced with a good will to believe, to a final view that God's grace to save us is irresistible, whether we are babes or adults. Even the baptised must struggle in this life with concupiscence and depend utterly on the grace of God to do the good they will. Chapter Four concerns ‘what must be attributed’ to God's power’ (p. 169) and ‘God's impact upon the will’: whereas Augustine initially describes ‘God's twofold help as consisting of bestowing knowledge and making the good attractive’, he later describes it in terms of re-orientating the will, and assisting us in the carrying out of the good; he also writes increasingly of God acting ‘unilaterally’ to convert the will (p.170). Furthermore, Augustine draws on biblical texts such as Joshua 7:12 and 1 Kings 12:15 to argue that God may incline the will of those who have chosen evil from bad to worse, though not ‘in a way that violates justice’ (p. 217).

Kantzer Komline then explores further in Chapter Five how Augustine's account of human willing is deeply informed by Scripture and its narrative of God working on the human heart, which Augustine increasingly and controversially identifies with the will as ‘permeable’ to divine influence’ (p. 255). Whereas Pelagius conceives of the will primarily as a faculty deployed one way or another in a series of choices for good or ill, Augustine understands it as a disposition and ‘root’ of action. A good will is understood as the love of God, and as deriving from faith in God (pp. 246 and 251). Chapter Six then looks at the specifically Christological dimension of the good will. By the time he composes the Contra sermonem Arrianorum in around A.D. 419, and because of his need to address Homoian Arian arguments, Augustine stresses the full conformity of Christ's human will with the divine will shared by Father and Son (pp. 294–298). Christ shows the unmerited nature of grace, models the good will which prioritizes justice over power, and restores and upholds a good will in the believer by ‘captivating’ her with delight in the truly good. In this latter role, the Lord's Prayer has a central place in its call for forgiveness and willingness to forgive others, as well as its petition not to fall into temptation and hope for final deliverance from evil (pp. 312–14).

Chapters Seven and Eight study, respectively, the relation of the Holy Spirit to the human will and human good will as it will be at the eschaton in the Kingdom of Heaven. The Spirit by its presence pours out ‘the love of Christ in our hearts, thereby setting our wills afire to delight in and love God, to freely choose the good, and to obey God's commandments’ (p. 336). In heaven the saints are rewarded with a perfected good will that securely enjoys the highest good which is its object. Fully freed from sin and evil desires by grace, they are like God in being unable to sin. They ceaselessly praise God in remembrance of their liberation from an evil will by Him in Christ (pp. 400–409). A brief conclusion recaps the history of Augustine's understanding of the human will before finally assessing the ‘novelty’ of Augustine's thought in relation to ‘philosophical sources from outside the Christian tradition, earlier Christian writings, and crucial verses and pericopes from scripture’ (p. 419). Augustine's account of voluntas is similar to but not identical with the Stoic notion of impulse or horme and is far more complex in its theologically differentiated account of the will with respect to different stages of salvation history. While Augustine's early defence of free will drew especially on earlier Christian tradition, Augustine also ‘appealed to Cyprian repeatedly to support his teaching on the limits and capacities of human willing’, when the will is dependent on God's help to turn from being unwilling to willing (p. 421). St Ambrose was another important source on whom Augustine drew in articulating his own position, but most important was the support Augustine found in Scripture, above all in St Paul. From these interrelated sources Augustine developed an account of the human will novel in the decisive role played by the triune God as its creator, redeemer, and rewarder, and in linking the will to the heart.

One recurrent feature of the book, and a potential weakness for some readers, is that major scholarly disputes or differences on how to read Augustine's texts are repeatedly relegated to lengthy footnotes (see, for example, the support for Wetzel rather than Carol Harrison in reading De moribus ecclesiae at pp. 37–38 n. 67) and not necessarily assessed on their merits (see for example, p. 65 n.16, and p. 67 n.20, and p. 142, n.60). This will not help students in learning to assess opposing readings. At the same time, a praiseworthy desire for clarity results in the main text being overly long and repetitious. Nonetheless, despite these drawbacks, this is a thorough and welcome presentation of a major topic in Augustinian studies with which future scholars should engage and with which they will find it hard to disagree.