Finally, Hume’s against the notion of necessary existence have obvious relevance also for Descartes’s effort, in Meditations III, to prove that God necessarily exists by way of reasoning from our (innate) idea of God. Since a priori any thing may cause any thing, it follows that even if we had an idea of a perfect being there would be no basis for the claim that God must be the source of this idea. Similarly, since we have no (abstract) idea of existence, distinct from the conception of particul