As set out in the acknowledgements this monograph is the outcome of many years of doctoral and postdoctoral research. Its argument is ‘that “Pelagianism” never existed’ except as ‘a composite fiction created for polemical purposes’ (p. xiii). This argument is developed in seven chapters. Chapter i outlines how Pelagius’ teaching was distorted and reduced to a caricature by polemical authors and his person vilified to undermine his credibility (pp. 1–28). Chapters ii and iii both carry the self-explanatory title ‘Pelagius did not invent anything: all the teachings in his writings had already been widely disseminated in ascetic paraenesis’. The chapters demonstrate in intricate detail how most of the tenets that were attacked as heretical in Pelagius’ writings (for example, the innate goodness of human nature and human ability to do good out of free will even after the Fall) can also be found in such orthodox (ascetic paraenetic) works as Athanasius’ Life of Antony, which circulated in several Latin versions, and in some of Jerome's biblical commentaries (pp. 29–196). Chapter iv sets out that no organised ‘Pelagian’ movement ever existed and that no single individual ever stood for all the teachings that were identified as ‘Pelagian’ (pp. 197–217). As mentioned in the introduction, ‘Pelagianism’, especially in the official documents that condemned it, for example the canons of the African bishops of the end of April 418, or Zosimus’ Tractoria of June 418, from all we know about the latter, was a ‘composite’ entity, not a coherent, systematic, body of doctrines developed by a single teacher and followed by an organised group, or church. It is therefore, as chapter v discusses, difficult to classify as ‘Pelagian’ writings that were not already classified as such during the controversy around 418. However, due to the disparity of that material, scholars have not been able to offer a clear and simple definition of ‘Pelagianism’ that would include all the aspects that have been identified as ‘Pelagian’. Furthermore, over time the grounds of the debate shifted, which gave rise to theological positions that were later (in the seventeenth century) labelled ‘semi-Pelagian’ (pp. 225–8). Any texts containing ascetic paraenesis, Bonner concludes, could potentially be identified as ‘Pelagian’, and many such texts existed in medieval monastic libraries. On the other hand, many such texts were attributed to orthodox authors, especially Jerome, and even Augustine. But until they were deemed pseudepigraphic by modern critics no ‘Pelagian’ features were identified in them. As Bonner points out, ‘medieval monks were strikingly unable to see a difference between Jerome's letters and Pelagius’ (p. 259). Chapter vii demonstrates this in some detail on the basis of manuscript evidence (pp. 288–301). Before that, in chapter vi, Bonner asks why and how ‘Pelagianism’ was ‘deliberately invented’ (p. 260). Augustine is cited in this context, and a particular Latin strand of Pauline exegesis represented by Marius Victorinus and Ambrosiaster, which in its anti-Jewish tendency placed a strong emphasis on faith (sola fides) as opposed to the law (p. 264). To explain the ‘how’ Bonner invokes ‘interactionist theory’, also known as ‘labelling theory’, and draws a comparison to the controversy about ‘Modernism’ in the Roman Catholic Church between the 1870s and 1940s (pp. 266–80). The chapter concludes with some remarks about how the ‘myth’, once created, ‘gained traction’ in the fifth century, ultimately to persist until the present day. A conclusion (pp. 302–7), an appendix containing an excerpt from Ambrosiaster's commentary on Romans ix.11–16 (pp. 309–13), bibliography (pp. 315–28) and index (pp. 329–42) complete the volume.

Undoubtedly, this is a very learned study intended, it seems, as a contribution to a longstanding and wide-ranging discourse about the problematic origins and use of the term ‘Pelagianism’. But its central argument that Pelagianism was a ‘myth’ is flawed. Its most substantial chapters (ii, iii and vii) are not about Pelagianism as a myth but about the ascetic paraenetic character of ‘Pelagian’ themes as they can also be found in ‘non-Pelagian’ works such as Athanasius’ Life of Antony and as is evidenced by the medieval manuscript tradition, both the scale of transmission of works by Pelagius and marginalia pointing to the orthodoxy of these works. Here the study makes an original contribution. But the attempt to force these findings into a myth-debunking argument risks devaluing them. Why is it necessary, for example, to insist that Pelagius ‘did not invent anything’? Does this not risk diminishing one of the leading and most original ascetic theoreticians and practitioners of his age both in East and West? Even by its own standards the myth-debunking argument falls short. For example, there is no critical discussion of the use of concepts such as ‘myth’, ‘fiction’ or ‘invention’. These terms are used interchangeably. But they are different concepts and none of them necessarily means that ‘“Pelagianism” never existed’ (p. xv) or ‘was a deliberately invented fiction’ (p. 302). Furthermore, chapters i and vi separate topics that belong together: Augustine's construction of ‘Pelagianism’ as a heresy (chapter i) occurred in a particular historical and church-political context (chapter vi). While this does not justify the condemnations of 418 and 431, it explains these historical events. Because of these events ‘Pelagianism’ as a heresy was neither a myth nor an invention or a fiction but a legal, political and theological reality. Writings attributed to Pelagius and others identified as Pelagians were suppressed and those who wanted to save them had to resort to subterfuge, for example by attributing such works to orthodox authors. Pelagianism was by far not the only ‘heresy’ to which this applied. For example, it was recently discovered that the work De incarnatione et deitate Christi ad Ianuarium (CSEL ic. 169–214), which throughout the Middle Ages and far into the early modern period was thought to be by Augustine, is in reality a collection of excerpts from Origen's De principiis. ‘Origenism’, too, was a heresy, but works of Origen were transmitted, some under the name of orthodox authors. The fact that this was done does not make the heresy less real. Finally, because of the historically contingent nature of Pelagianism as a heresy Marius Victorinus and Ambrosiaster ought not to be depicted as contributing to its construction. In late fourth- and early fifth-century Rome it was possible for Pauline commentators to hold different opinions without being accused of heresy. It was not predetermined that Pelagius should end up as a heretic and Marius Victorinus and Ambrosiaster as orthodox. In light of this it is all the more astonishing that works by Pelagius are among the most copied of all patristic works (albeit pseudonymously, under the names of Jerome and Augustine), while very few manuscripts of works by Marius Victorinus and Ambrosiaster have survived.

In conclusion, were it not for the somewhat misguided focus on the argument that ‘“Pelagianism” is a myth’, this could be an excellent study on the ‘ascetic paraenetic’ character of Pelagian writings. Most of the issues raised by this study could be tackled from this angle: Pelagius’ success in Rome as a Pauline commentator and ascetic author and teacher; the potential influence of eastern asceticism and monasticism on Pelagius; the time and effort it took Pelagius’ enemies to condemn him as a heretic; the survival of his works, mostly pseudonymously, after the condemnation; the glut of ‘Pelagian’ writings (i. e. works in the ascetic paraenetic style akin to Pelagius’) extant despite the condemnation; the scale of the manuscript transmission and the existence of marginalia that show awareness of Pelagius’ authorship and a continued appreciation of his ascetic theology in medieval monasticism. For the continued pursuit of all these questions this study offers important and valuable new impulses and perspectives, and can therefore be recommended as a substantial contribution to the study of Pelagius and his works and thought.