Those who might be put off by the subtitle the author instructs: “Do not expect a ‘rise of Western rationality’ essay, nor discussion of whether the ‘Protestant Ethic and the Spirit of Capitalism’ had medieval origins” (1). What is the book about? The answer does not come easily. The author acknowledges that “parts of the foregoing chapters will have passed too close to the rocky ground of detailed medieval scholarship for the comfort of some readers; this conclusion may seem to go up to an unpleasantly high altitude of abstraction” (164). I admit that I consider the whole book from the second point of view. It is not about history or medieval religion, though d'Avray illustrates his views by copious examples drawn from medieval sources.

My problem is the ill-defined, slippery use of the word rationalities. The author defines rationality as “thinking which involves some general principles and strives for internal consistency, where the key causes of the idea or actions are different from the reasons the person or people would give for it, even to themselves” (2). This sounds more like “rationalization” than “rationality.” It is also unclear how d'Avray knows the “real explanation” (2) or “real motivation” (9) behind this self-deception. He affirms that “modern scholars can safely assume” that the belief in question was not “warranted by actual facts” (3).

The author's aim is to elucidate how “different forms of rationality . . . relate to and react with one another” (2). These forms are “conviction rationality, also called value rationality, and instrumental rationality” (164). I would simply—perhaps too simply—call these ways of thinking beliefs and methods to realize those beliefs.