 More generally, we should distinguish issues of epistemic and ontological dependence. In the final analysis, Descartes thinks he shows that the occurrence of thought depends (ontologically) on the existence of a substantial self – to wit, on the existence of an infinite substance, namely God (cf. Med. 3, AT 7:48ff). But he denies that an acceptance of these ontological matters is epistemically prior to the cogito: its certainty is not supposed to depend (epistemically) on the abstruse metaphysics that Descartes thinks he eventually establishes. (See Vinci 1998 for an alternative reading.)