Marin Mersenne: La Vérité des sciences contre les Sceptiques ou Pyrrhoniens

This work of 1625 comes from an early stage in Mersenne's career, before he became the centre of a dynamic intellectual network, and, as Descotes points out in his admirable introduction, it has therefore often been underestimated (although it is discussed in Popkin's History of Scepticism). Yet it deserves to be explored. Mersenne's preface represents scepticism as a strategy promoted by libertins targeting youthful pleasure-lovers: by sapping their faith in the sciences they hope to weaken their religion. Formally, the text is a dialogue, with, in the first book, the sceptic being confronted by an alchemist and a Christian philosopher. The two former are used to demolish each other, and the Christian philosopher picks up the pieces (an anticipation, Descotes suggests, of Pascal's technique in the Entretien avec Monsieur de Sacy). After Book i, the alchemist disappears and the sceptic dwindles almost to nothing. For those interested in the history of scepticism, Book i is therefore the most rewarding. In Chapter 11, the Christian philosopher gives a succinct summary of Pyrrhonism, noting the technique of mutually destructive arguments, and enumerating the famous tropes, which he refutes as he goes along. However, the sceptic carries on the fight as long as he can using Pyrrhonist manœuvres, already present in the Apologie de Raymond Sebon: attempts to justify knowledge involve a vicious circle, or an infinite regress from one reason to another. The validity of the syllogism, and Bacon's critique of it, are also discussed, as is the Baconian taxonomy of idols. The detailed and methodical nature of the discussion means that Mersenne is doing far more than merely restating Montaigne's presentation of Pyrrhonism, and there is much of interest in his attempts to rebut it. However, not content with a general refutation, he aims also to provide a specimen of certain knowledge, in the form of an abridgement of mathematics, which occupies the rest of the work and deals with arithmetic, algebra, geometry and trigonometry. As Descotes observes, Mersenne's text thus allows us to gauge 'ce que l'honnéte homme pouvait savoir et comprendre des mathématiques du temps' (p. 105). Mersenne lays especial stress on the musical applications of mathematics and also celebrates its technological benefits. It enables us to imitate the divine handiwork, but Mersenne sees this not as encroaching on the Creator's sphere, but rather as affording us further reason to admire him. And the applications of mathematics are not only technological; Mersenne uses the concepts of arithmetical and geometrical progression to analyse the effects of grace, and to distinguish democratic from aristocratic states (monarchy, the best of all forms, being based on harmonic proportion). This excellent edition, fully annotated, offers us access to a text that not only offers important insights into Descartes and Pascal, but constructs an intellectual world fascinating in its own right.