Medieval religious rationalities is a challenging but rewarding book. David D'Avray sets himself the task of applying to medieval religion Max Weber's categories for the analysis of reason. Above all, D'Avray concerns himself with the ways in which popes, canon lawyers and theologians squared received doctrine and practices with observed reality, thorny legal issues, and internal or external challenges such as the preaching of St Francis and rediscovered Aristotelian texts. D'Avray argues that Weber's categories, especially the two polarities of value/instrumental rationality, and formal/substantive rationality, are helpful methodological tools in explaining the Church's success over a full millennium in both handling its own affairs and conducting its mission in the world. The author's own research on preaching, marriage and the way in which the papal court exercised its legal function equips him admirably to provide illustrations and case studies of the numerous occasions when churchmen faced such apparent challenges to rationality as miracles, the Trinity and penance. There is much to admire in the book. The pages on the reception of Aristotle in thirteenth-century Paris are revealing and chapter v, on papal justice, advances an intriguing explanation of how the curia managed to exercise such a pervasive legal influence across Christendom with such a small personnel. Throughout the book D'Avray's style is engaging, and he takes pains to explain technicalities for the benefit of non-medievalists.

Wisely, D'Avray took the decision to place the bulk of the theoretical exposition in a companion volume, Rationalities in history: a Weberian essay in comparison, which is published simultaneously by Cambridge University Press. Medieval religious rationalities can be read on its own though D'Avray helpfully cross-references his two texts. Students of comparative religion will be attracted by these books and it is likely that their thesis will be much discussed, but I have found that what sticks in the mind are individual passages of analysis and insight rather than the overarching argument.