  Here Descartes develops his earlier analogy between the (so-called) ontological argument and a geometric demonstration. He suggests that there are some meditators for whom God’s existence is immediately manifest; for them God’s existence is akin to an axiom or definition in geometry, such as that the hypotenuse of a right triangle subtends its largest angle. But other meditators, whose minds are confused and mired in sensory images, must work much harder, and might even require a proof to attain the requisite clear and distinct perception. For them, God’s existence is akin to the Pythagorean Theorem. The important point is that both kinds of meditators ultimately attain knowledge of God’s existence by clearly and distinctly perceiving that necessary existence is contained in the idea of supremely perfect being. Once one has achieved this perception, God’s existence will be manifest or, as Descartes says elsewhere, “self-evident” (per se notam) (Second Replies, Fifth Postulate; AT 7: 164; CSM 2:115).