The interpolation in 1 John v of a passage about the three heavenly witnesses that are one – the Father, the Word and the Holy Spirit – excited theological passions from the early sixteenth century until into the nineteenth. Should this passage, known as the Johannine comma, be admitted as a biblical proof text for the doctrine of the Trinity, or should it be dismissed as uncanonical? The comma first appeared in two seventh-century Latin Bibles copied in Spain. Only in 1516, in Erasmus’ notes to the first edition of his New Testament, did the comma achieve its disputed status. Since Erasmus did not find it in any Greek manuscripts, he omitted the comma from his correction of the Latin Vulgate. His decision drew sharp criticism from the English theologian Edward Lee. When a Greek manuscript, now known as the Codex Montfortianus at Trinity College in Dublin, containing the comma surfaced in England in 1521, Erasmus restored the comma in the third edition of New Testament (1522). It remained in the fourth (1527) and fifth (1535) editions. The latter edition contributed to the formation of the so-called textus receptus of the New Testament. Although he restored the comma, Erasmus surmised that the Codex Montfortianus deliberately followed the Latin reading. Grantley McDonald rightly points out that Erasmus ‘always considered’ the comma ‘an intrusion’ (p. 56).

Erasmus’ deletion and subsequent insertion of the comma constitute the source of its fascinating, controversial history, which McDonald meticulously traces with elegant prose and accessible erudition. Defenders of the comma maintained that Erasmus ultimately accepted its authenticity, while critics pointed to his doubts. His scholarly reputation fueled controversy. Cornelis Adriaenssen, a Franciscan friar, denounced in 1569 the ‘devilish books of that damned Erasmus of Rotterdam’, who had abetted anti-Trinitarianism (p. 89). McDonald's description of the assessment of one early eighteenth-century defender, David Martin, a Huguenot pastor in Utrecht, holds for the entire early modern debate about the comma: Erasmus was responsible ‘for stirring up this unfortunate hornets’ nest’ (p. 229). Thomas Emlyn, an English anti-Trinitarian, was Martin's adversary in a clash that ‘attracted attention from all over Europe’ (p. 231). He observed, as McDonald aptly points out, ‘that Martin had shifted the focus of the debate to Erasmus’ character, his trustworthiness, his motivation, and his readiness to resort to pragmatic compromise’ (p. 230).

By the early eighteenth century, a myth drew Erasmus’ character into the debate about the comma. Erasmus supposedly had promised Lee that he would restore the comma if it existed in one Greek manuscript. In 1980, in an article in Ephemerides Theologicae Lovanienses, Henk Jan de Jonge exposed and exploded the myth, whose origin he could trace only to 1818. McDonald, his student, locates ‘the seed from which the myth of Erasmus’ promise grew’ (p. 151) in the way in which Richard Simon told the story about Erasmus and the comma in his Histoire critique du texte du Nouveau Testament (1689). In a final apology for the comma published in 1721, Martin ‘presented the first fully developed narration of the myth’ (p. 236).

McDonald's book successfully shows that from sixteenth-century Bibles to ‘the Catholic modernist crisis’ (p. 300) at the end of the nineteenth century, the philology of biblical criticism was ‘not an abstruse scholarly exercise’ (p. 12). The battle for and against the comma enlisted the eager pens of theologians, biblical scholars and other intellectuals. McDonald is primarily interested in English arguments about Trinitarian theology from the Civil War to the late eighteenth-century Enlightenment.

His methodology of explicating reactions to the comma of a long succession of scholars from John Milton to Edward Gibbon and his contemporaries underlines the importance of human agency in the history of ideas. This does not amount, however, to what McDonald calls ‘a social history of the debate’ (p.12). Despite brief references to early modern English anti-Catholicism and to the reach of the debate about the comma ‘into all parts of English society’ (p. 290) in the nineteenth century, Biblical criticism in early modern Europe remains a highly accomplished work of intellectual history. McDonald deftly unfolds a complex and fascinating controversy of great moment in the history of Christian ideas.