 The definition of metaphysics given in the Quaestiones is strongly reminiscent of Aristotle’s Metaphysics E1—where “prime philosophy” is conceived as strictly concerned with the separated or immaterial substances, thus with the “theological” realm. Jean-Luc Marion (1994) pointed out that although Mersenne, in several places, acknowledges formally another traditional object for metaphysics, that is the “ens quatenus ens” (the abstracted Being as such, whose science applies indifferently to all beings, created or uncreated), he seemed reluctant to give this science (that we now call ontology) any substance. In a striking passage from the Quaestiones, Mersenne said that “Being” is a name that suits God better than any of the creatures: