Abstract: This book investigates the common medieval belief that magic could cause impotence. Because impotence was a ground for annulling a marriage in medieval canon law, it received a large amount of discussion in the Middle Ages, and many of these discussions also described how impotence could be caused by magic. Chapters 1-4 trace the development of ideas about magically-caused impotence from the ancient world into the 12th century, arguing that medieval writers only gradually came to distinguish impotence magic from other forms of love magic. Chapters 5-9 then analyse the main kinds of sources which mentioned impotence magic in the late Middle Ages: magical texts, confession manuals, canon law commentaries, theology commentaries, and medicine. A comparison of these sources reveals that medieval writers held surprisingly diverse opinions about what magic was, how it worked, and whether it was ever legitimate to use it. Finally, in Chapter 10, the book shows how ideas about impotence magic were affected in the 15th century by new fears of demonic witchcraft. The book argues that many authors who discussed impotence magic were interested in popular magical practices, and so it acts as a case study of the relationship between elite and popular culture in the Middle Ages. It emphasizes the importance of the 13th-century pastoral reform movement, which sought to enforce more orthodox religious practices. This movement brought churchmen into contact with popular magic, and encouraged them to write about what they saw.

Keywords: canon law, confession manuals, marriage, medicine, popular culture, theology, witchcraft