In a footnote on page 73 of his The Natural and the Supernatural in the Middle Ages, Robert Bartlett promises, “There is a $5 standing bet for anyone finding any evidence of the question [of how many angels can dance on the head of a pin] being asked in the Middle Ages.” This comment perfectly encapsulates the spirit of the book, in which Bartlett explores the tension—and the overlap—between matters of faith and matters of science in the Middle Ages, all the while debunking modern misconceptions of medieval sophistication (or lack thereof) and encouraging further exploration on the part of his audience. These four relatively brief essays arose out of the Wiles Lectures that Bartlett gave at the Queen's University of Belfast in 2006, and that genesis is evident in the engaging and often wry tone of Bartlett's writing, which has the effect of making complex topics quite accessible and engrossing.

The scope of The Natural and the Supernatural in the Middle Ages is expansive, as Bartlett himself acknowledges when he reveals his approach in the preface: “My title is fairly grandiose, and clearly these lectures do not aim at comprehensiveness but, I hope, at illuminating examples and general considerations” (x). The first essay, “The Boundaries of the Supernatural,” concerns itself with those “general considerations” as a means of providing background for the following three essays, which all take a somewhat narrower approach. Bartlett sets up what he calls the “central dualism: the natural and what is beyond nature” (7). The investigation of miracles during the church's process for canonization provides the context for Bartlett's exploration of the supernatural's borders and boundaries. During these investigations, the church often drew very fine and occasionally confusing distinctions between supernatural miracles and demonic “natural” magic. Tracing a growing attempt to confine the supernatural, Bartlett concludes that the medieval period participates in what Max Weber calls the “disenchantment of the world,” an increasingly analytical approach to the natural world that makes the medieval period not “the cartoon ‘Other’ to modern pragmatic rationalist society but … a stage on the path to it” (32).

With the consciousness of conflicted categories setting the stage, Bartlett's next two chapters look at specific phenomena that simultaneously engage with both the natural and the supernatural. “The Machine of the World: Ideas of the Physical Universe” investigates the ways in which medieval thinkers employed “both the logic of the elements and the logic of the spheres” (39). The former is addressed by three medieval writers who attempted to understand the disposition of land and water on earth, particularly as it related to the biblical creation story and salvation history, and the latter by an investigation of the medieval understanding and use of solar and lunar eclipses. The case of eclipses provides a particularly striking case study of the conflict between natural and supernatural: while eclipses were predictable astronomical phenomena and thus clearly linked to the natural world, they were nevertheless also omens and signs to be interpreted. Crusaders seem to be particularly invested in astronomical signs as they related to success in battle, although interpretation of the eclipse was often made retroactively.

In his third essay, Bartlett revisits medieval figures beloved by modern scholars: the cyno cephali, or dog-headed men. Because they straddled the boundary between human and animal, they caused a conundrum in the medieval understanding of the soul. The ninth-century monk Ratramnus considers the necessary qualities of humanity and concludes that the dog-heads possess them because they live communally, wear clothes, and farm, and are, therefore, worth converting. More interesting, however, are the consequences of the crusaders’ penetration of the mysterious East, with its concomitant discovery that the cynocephali were nowhere to be found. These explorers make the important discovery that “monsters are always elsewhere” (106). The external investigation of the natural and supernatural—by both Bartlett and by the medieval explorers—is turned inward to become an internal examination of self and the Other. Bartlett's frequent use of manuscript illustrations to provide visual clarification and enhancement of some of the more fantastic elements of his discussion are particularly effective in the chapters on eclipses and the cyno cephali.

Although each of Bartlett's essays stands on its own, Bartlett deftly revisits themes from earlier chapters as the book progresses, so that the argument about the complexity of medieval beliefs builds progressively to a climax with his portrayal of Roger Bacon's work in 1267, when Pope Clement requested Bacon's advice about the arrival of the Antichrist, which both believed was imminent. Bartlett presents Bacon as immensely egotistical, convinced of his own brilliance, and perhaps slightly paranoid in his dealings with others. However, Bacon was also surprisingly modern, a man who valorized science, math, and foreign-language education, and was complex and sophisticated in his reasoning and thinking. He was fascinated by the conjunction of the natural and the magical and insistent that his work, with its belief in the power of incantations and fascination, did not in any way condone magic but instead distinguished itself as the work of an intelligent man working through “natural power” (144). In addition to showing off Bartlett's ability to reveal the complexity of characters as well as issues, Bacon seems to demonstrate clearly that the overlap between the natural and the supernatural pervaded and perplexed even advanced and educated thought of the Middle Ages.

Although Bartlett's analysis of these overlaps and tensions is complex and thorough, it feels more like a starting point than the definitive word on the subject. Bartlett himself readily admits that most of his source material is in Latin from the High Middle Ages (1), making it the province of the educated and, often, the religious of the era, and creating, therefore, plenty of room for the future investigation of the same questions in vernacular and lay sources throughout the entirety of the Middle Ages. Bartlett asks important questions about the supernatural and natural world in the Middle Ages, and in his answers he establishes guideposts for the continuing investigation of complex and major issues in medieval belief.