 Claims of infallibility and omniscience concern general relations between beliefs about mental states and those mental states themselves. The most famous philosophical argument involving self-knowledge, Descartes’ cogito argument (Descartes 1641/1895), does not concern these general relations. Instead, it concerns the certainty of a particular instance of belief. Descartes aims to demonstrate that, so long as you are carefully attending to your own thoughts, you can know with certain that you’re thinking—and, hence, that you exist. This can be certain even if there is a supremely powerful evil genius who controls your thoughts and seeks to deceive you.