 Mersenne was indubitably an heir to the Thomistic view of a necessary synthesis between Christian faith and philosophy. As expressed in the praefatium of the Quaestiones in Genesim, it is “a duty of the learned to refute atheists”, the tacit assumption being that “true philosophy never contradicts the teachings of the Church” (ID II: 490–1). This synthesis was vindicated in the rather troubled political, and religious context of early seventeenth-century France, which still bore the scars of half a century of religious wars, and appeared exposed and vulnerable to what Catholics considered a severe crisis of orthodoxy, raging on all fronts. A rising tide of libertines, deists, skeptics, cabbalists, alchemists, and naturalist metaphysicians, all more or less consciously in league with the Protestants, seemed to Mersenne on the verge of overwhelming the “true” Christian faith. Mersenne often pointed out the connection between Protestantism and the various forms of heterodoxy and atheism: the Calvinist belief in predestination insensibly drives men toward superstition and atheism, as it appears more difficult to believe that God wants our damnation, than to represent Him as a “cruel Saturn who devours his children”, or simply to own that there is no God at all (ID II: 589). So, Mersenne’s early-interventions may be seen as taking part in the larger movement of “re-catholization” of the French state after the pacification allowed by the Edit de Nantes. In this regard, Mersenne’s advocacy of a harmonious conciliation of faith and reason was not without similarities with a noted feature of Galileo’s “cultural program” in the same years: both wanted to contribute to the Counter-Reformation, and both defended the specific idea that Catholics should not leave to Protestant heretics the monopoly of reason and scientific knowledge. Mersenne was however wary of any anti-Aristotelian philosophical novelties (including those of Galileo himself), as he saw them as ipso facto dangerously verging towards contesting religious truth. According to Garber (2004), the Aristotelian framework, particularly prominent in the first works, was adopted not so much for its philosophical virtues as such, but rather as a rampart of orthodoxy, as a tried doctrine, that has long proved its ability to be harmoniously conjoined with Christian faith, and as it were to protect it. By contrast, alternative ways of thinking offered no such guarantee against heresy, as they were often defended with a zeal that was dangerously close to fanaticism. As Mersenne stated in the preface to the Quaestiones (1623):