Neil Tarrant is one of a growing group of scholars seeking to correct our understanding of the role of ecclesiastical censorship in the development of early modern thought, and this work contributes to that project. The book's title links it more specifically to recent works on the Roman Inquisition's multifaceted influence on early modern science, ranging from special issues of Annals of Science (2020) and Early Science and Medicine (2018), to Ugo Baldini and Leen Spruit's massive compilation of inquisitorial documents, to more focused studies such as Hannah Marcus's Forbidden Knowledge: Medicine, Science, and Censorship in Early Modern Italy (Chicago: University of Chicago Press, 2020). Such works have taken the topic far beyond Black Legend caricature and an unhealthy obsession with the Galileo Affair.

In his own words, Tarrant's contribution here is “essentially an intellectual history of Thomist thought on magic” (18), almost exclusively within the Dominican order. He seeks to connect that story to the history of the inquisition of magic in northern Italy and to situate both in the context of ecclesiastical debates and developments from the later Middle Ages through the early Reformation era. Occasionally, Tarrant's zeal to contextualize causes his detailed reviews of struggles over papal authority, mendicant privileges, and competing visions of ecclesiastical reform to overshadow the ideas themselves. The connection to “the Roman Inquisition and the boundaries of science” promised by the book's subtitle arrives at the end of the work, when Tarrant briefly makes his case for the eventual consequences of the intellectual developments he traces.

Tarrant's core argument is that an identifiably Dominican approach to distinguishing between licit and illicit magical practices emerged in the later Middle Ages, was then promoted by Dominicans and their allies as part of the Observant reform movement, and finally gained greater influence when the Order of Preachers took on key roles in the newly reorganized Roman Inquisition in the 1500s. However, Tarrant proposes that straightforward narrative with many qualifications about resistance to the Dominican approach and its ultimately limited impact. Tarrant examines relatively few trials, always through printed sources, and they rarely display clear connections with the learned debates. This is much more a history of judicial theory than of actual process, despite Tarrant's occasional quarrels with other historians’ interpretations of trial trends.

The book is divided into two parts, plus an introduction and conclusion. The shorter first part outlines the “Medieval Foundations” of Tarrant's narrative. He casts the growth of the mendicants and the development of the papal inquisitor hereticae pravitatis as key to the transformation of the problem of magical misconduct from one of superstition into one of heresy. Significantly, though, not all of what Tarrant calls the “operative arts” (1), by which he generally means learned magic, was universally condemned. Tarrant highlights the work of Albertus Magnus and—more importantly—Thomas Aquinas in developing criteria for evaluating magical activities. Aquinas's central criterion was causal: effects worked using natural powers were legitimate whereas naturally impossible effects were demonic, whether or not the operator explicitly sought demonic assistance. Tarrant promptly caveats this claim by noting that Aquinas could be ambiguous and self-contradictory, and his ideas were contested within, let alone outside, his order. For example, Tarrant sees Nicholas Eymerich's Directorium inquisitorum as offering a popular alternative focused on action rather than causation: activities with invocations indicated a demonic pact, whereas activities without such ritual elements were legitimate. In sum, what counted as legitimate practices remained contested at the end of the Middle Ages.

The second part of the book focuses on the prosecution of magic in the context of conciliarist challenges to the papacy, the rise of the Observant mendicants, and various sixteenth-century reform movements. Observants’ reform efforts, Tarrant argues, resulted not only in the elaborated witch stereotype that other historians have described but also a shift by Dominican inquisitors away from Eymerich's action-focused approach to evaluating magical practices to a more Thomist causal approach. The practical impact of this change again remained limited, at least as measured by Italian inquisitorial prosecutions. However, the new Index and revamped Inquisition eventually gave the Dominicans means to spread their approach through the church more generally. This is where Tarrant sees the real impact of Dominican thought: a “radical transformation of the criteria used in the censorship and prosecution of magic” that resulted in the Roman Inquisition's claiming the “right to determine nature's limits” and hence to define the scope of phenomena open to philosophical inquiry (202). And yet, when Tarrant ends his survey, the boundaries of the natural and the Inquisition's role in defining it remain contested, entangled in longstanding disputes over papal power and mendicant privileges, among other issues.

What Tarrant shows most clearly are the medieval roots to the most famous era of inquisitorial prosecution of magic. In this longer-term view, the oft-invoked inquisitorial turn away from the pursuit of Protestants to a focus on magical misconduct can be seen rather as a return to an earlier concern and the related struggle to distinguish between legitimate and illegitimate activities. Tarrant strives to impose a teleological plot onto this knotty intellectual history, but it is not clear that such linearity is needed: the shifting patterns in the never-resolved debates about categories of knowledge and practice and about the boundaries between natural and demonic are important in themselves, even if they did not produce a distinct redefinition of the boundaries of science in practice. Moreover, Tarrant's efforts to connect these intellectual shifts to broader and longer-term institutional changes in the church are valuable. This is where the book's strengths lie: bridging the medieval–early modern divide to bring into conversation histories of magic, inquisition and censorship, and ecclesiastical reform.