The topic of certitude is much debated today. On one side, commentators such as Charles Krauthammer urge us to achieve "moral clarity." On the other, those like George Will contend that the greatest present threat to civilization is an excess of certitude. To address this uncomfortable debate, Susan Schreiner turns to the intellectuals of early modern Europe, a period when thought was still fluid and had not yet been reified into the form of rationality demanded by the eighteenth and nineteenth centuries.

Schreiner argues that Europe in the sixteenth century was preoccupied with concerns...