Defining Nature’s Limits: The Roman Inquisition and the Boundaries of Science, by Neil Tarrant

This book is a valuable contribution to the history of the relations between science and religion in Christianity. Despite the subtitle, the book is not primarily about the Roman Inquisition, which was only founded in 1542. Spanning half a millennium, it is, rather, an account of the inquisitorial investigation of magic and ‘an intellectual history of Thomist thought on magic’ (p. 18) in medieval and early modern Europe (c.1000–1564). The book comprises seven chapters, which are divided into two parts: ‘Medieval Foundations’ (chs 1–3) and ‘Mendicant Reform and the Inquisition of Magic’ (chs 4–7). The introduction kicks off with an anecdote about the investigation of Giambattista Della Porta’s magical practices by the Roman Inquisition in 1577 in order to frame the book’s main questions: what were the boundaries of learned magic before the establishment of the Roman Inquisition, when were they settled, and how did they inform the prosecution of magic?

The introduction provides a good overview of the book’s central claims and structure. Neil Tarrant acknowledges his intellectual debts and engages with the works of variety of scholars, including Ugo Baldini, Leen Spruit, Christine Caldwell Ames, Edward Peters, John W. O’Malley, H Darrel Rutkin and Francesco Beretta, among many others. Following in the footsteps of John Tedeschi, Christopher Black, Baldini and Spruit, Tarrant claims, for instance, that ‘in theory, the Roman Inquisition’s power was significant, but in practice it was limited’ (p. 163). The most notorious absence in the book is arguably Hannah Marcus’s Forbidden Knowledge: Medicine, Science, and Censorship in Early Modern Italy (2020). Primarily concerned with the censorship of medicine, Forbidden Knowledge offers an overarching narrative of the rationale, praxes and consequences of Catholic censorship in the early modern period. By delving into the heated discussions around the compilation of the Index, the process of dispatching thousands of reading licences, and the practices of expurgation, Marcus offers a compelling and innovative account of the paradox of Catholic censorship embodied in the Roman Congregations of the Holy Office and Index. Notwithstanding a slight chronological overlap and their distinctive approaches, it would be beneficial to read the two books in conjunction, with Tarrant’s book serving as a prelude to Marcus’s fugue.

Throughout the book, Tarrant traces the influence and the different readings of Thomas Aquinas’s thought on magic, superstition, unbelief and heresy (first conveyed in the Summa contra gentiles and later developed in the Summa theologica) and argues that Aquinas’s views were paramount in the prosecution of magic from the thirteenth century onwards. Stemming from his earlier research on the censorship of magic, alchemy and astrology, here Tarrant covers a variety of printed sources, ranging from papal bulls to Church decrees, and from indices of forbidden books to trial records and inquisitorial manuals, including the influential manuals written by Bernard Gui (c.1323–4), Nicholas Eymerich (1376) and Jacobus Institoris and Heinrich Sprenger (1487).

The definition of boundaries, as the subtitle foretells, is a recurring theme of Tarrant’s monograph. Aquinas’s position on the manipulation of the natural world and the resort to the preternatural realm (i.e., the summoning of angels and demons to achieve a given purpose) provided the rationale for setting the boundaries between the lawful and the unlawful forms and uses of magic. Whereas Aquinas rejected geomancy, chiromancy, necromancy and other operative arts, he conceded that it was possible to make some astrological prognostications, in so far as they were derived from natural causes. The movement of the celestial bodies allowed the astrologer to make certain predictions, such as the occurrence of an eclipse, and uncertain ones, such as the forecast of droughts, famines or deaths. As Tarrant has already argued elsewhere, the theory of celestial influence famously propounded by Aquinas contradicted Augustine’s firm opposition to astrology. The arguments conveyed in the Summa theologica allowed for the endorsement of certain forms of astrological prognostications setting yet another boundary, one between lawful (or natural) and unlawful (or judicial) practices.

In the thirteenth and fourteenth centuries, the principles formulated by Aquinas regarding the boundaries of magic were incorporated in ecclesiastical documents, including papal bulls and inquisitorial manuals, most notably John XXII’s Super illius specula (1326) and Eymerich’s Directorium inquisitorum (1376). According to Tarrant, Eymerich’s hasty reading of Aquinas’s thought on magic informed the general ban placed on the operative arts in the Roman Index of 1559. After a quasi-unanimous slander across the confessional divide, the Index promulgated by Paul IV was revised at the Council of Trent (1562–4). Besides reducing the Inquisition’s overarching control over printing, the Tridentine Index introduced new principles that became deeply entrenched in Catholic censorship (i.e., the three classes of forbidden books, the ten general rules, and the prospect of expurgation). When it came to magic and divination, the Tridentine Index resorted not to Eymerich’s limited reading of Aquinas, but rather to the Angelic Doctor himself.

One of the central arguments of Tarrant’s book is that the Dominicans ‘embedded their reforming agenda into the first papal Index of 1559, including a new approach to the censorship of learned magic rooted in the thought of Thomas Aquinas’ (p. 171). This overarching claim is, nevertheless, convincing and attests to Tarrant’s success in presenting an intellectual history of Aquinas’s ideas on magic and superstition. In the conclusion, Tarrant declares that ‘my central contention in this book is that this transformation of the criteria of censorship of magic had a radical impact on the subsequent development of science’ (p. 202). Although most historians of science would agree with him on this, it would have been better to fully develop this claim a little further (pp. 201–4).

Tarrant deepens our understanding of the role of Aquinas’s intellectual legacy, the centennial discussions around papal supremacy and conciliarism, and the rise of the mendicants, especially the Dominicans, in the censorship mentality that characterised the early modern inquisition. Well researched, elegantly written and authoritative, the book provides an excellent example of a fruitful engagement between Church history, the history of magic and witchcraft, intellectual history, and the history of medieval and early modern science. Hopefully, it will become a landmark in the history of the complex relations between science and religion in the Western world.