 To realize this aim, Mersenne’s strategy was twofold: polemical and constructive. On the one hand he attacked his polymorph enemy with the rhetorical instruments of a skilled debater, using the weapons of the adversaries, or making one refute the other (as in the dialogue between the alchemist and the skeptic in the first book of La Vérité des sciences). Hermetic authors such as Robert Fludd, or cabbalistic Christians such as Giovanni Pico and Jacques Gaffarel were vehemently denounced, as they availed themselves of spurious allegorical interpretations of the Bible. Even when their reading of the Bible is not wrong, they are dangerous as they make people believe they can deduce a priori, or through divine inspiration, what can only be known a posteriori, through revelation and experience. Heretic tendencies were pointed out in the doctrines of the Alchemists, who, in the wake of Paracelsus’s Mysterium magnum, tried to give naturalist interpretations of Christian mysteries, such as the resurrection or the miracle of Creation. Mages, sorcerers, and adepts of esoteric mysteries such as the Rosicrucians prosper on men’s propensity to superstition. Naturalist metaphysicians—Bruno, Campanella, Pomponnazi—who endowed nature with creative powers, verge dangerously toward pantheism, casting doubt on creation, on the transcendence and freedom of God. A leading thread in all these criticisms, is the idea that the Catholic belief in miracles and mysteries, far from being superstitious, is much more attuned to sound reason than the doctrines that are opposed to it. A light knowledge of philosophy may induce some doubts, but the more one knows the sciences, the more these Catholic beliefs and mysteries are reinforced and may be vindicated against false religion and atheism. A smattering of knowledge in optics can for example cast doubt on the truth of divine epiphanies, but a better knowledge of this same science allows one to exclude the idea that miracles can be illusions caused by reflections or refractions and therefore makes more sensible their divine origin (QG: col. 522, 538). This sort of negative argument shows that Mersenne’s rationalist defense of religion allows for truths beyond the capacity of men’s reason. In this, Mersenne stand explicitly against the deist. Both allowed for “natural religion”, but whereas the deist denounced the superstition and anthropomorphism of popular belief, Mersenne reversed the attacks and denounced the far worse anthropomorphism of one who measures God by human reason: “it is feebleness of the mind, to believe that our finite understandings can comprehend the divine attributes or acts” (ID I: 318–9; see also ID I: 669–70, and Beaude 1980). This however should not be understood as revealing a secret inclination towards fideism: religion teaches truths which surpass reason, “not in destroying it, but rather in perfecting it” (ID I: 680).