In this chapter I argue the following thesis: 1) Descartes’s Meditations never formulate the problem of God’s existence as it is required by the precepts of order; in particular, the only problem of existence posed by Descartes after the classification of thoughts in the Third Meditation does not concern God directly, but generally aliqua res. 2) Though Descartes qualifies the two proofs of the Third Meditation as a posteriori, they cannot be considered as homologous in their structure to the traditional a posteriori proofs: they both—and the second in particular—contain components that are truly a priori. 3) The proof of the Fifth Meditation, as it starts from the true definition of God and God’s essence, does not constitute a quoadnos version of the a priori demonstration belonging to mathematics, but is, in a strict sense, a potissima demonstration that is at least as evident as those of mathematics.