 Voluntarism was an important feature in Mersenne’s apologetics. Against what appeared to him dangerous necessitarian tendencies in Renaissance naturalist philosophies, he repeatedly advocated God’s essential freedom in regard His creation. God chooses to exert his efficient, transitive causality in whatever way he will. This for instance explains why Mersenne always opposed the idea of an infinite universe. An infinite world, of the kind postulated by Giordano Bruno, would be very close to a necessary emanation of God, but it is neither required of God’s infinite power, nor does it agree with the nature of a created thing :