 Mersenne’s attitude towards skepticism was complex, changing over time and somewhat ambivalent. In L’Usage de la raison—a recently rediscovered booklet from 1623, whose authorship does not seem questionable—one finds arguments against the vanity of the sciences that are strongly reminiscent of those expressed around the same time by “Christian skeptics”, such as Montaigne and Charron, or even Cornelius Agrippa, authors whom Mersenne sternly criticized in his next publications. Thus, in the “Dedicatory Epistle to Madame de Vitry”, the Minim suggested that our time is badly employed in studying the sciences, which are plagued with insuperable uncertainty: