This chapter aims to provide the foundations for Descartes's view that there is a real distinction between mind and body. According to Descartes, x and y are really distinct if x and y are substances and can exist without each other. It is argued that the possibility adumbrated in this definition is weaker that genuine possibility of disparate existences, but it is nevertheless sufficiently strong for vindicating Descartes. Even if it is not really possible that the mind and body lead separate existences, it is logically consistent with what the mind is, being a thinking thing, that it exists without any extended body and even without the specific body that belongs to a person. This conclusion is teased out from careful scrutiny of Descartes's three main arguments for the existence of a real distinction: the argument from possibility, the argument from conceivability, and the argument from whatness (essence). Arnauld's fourth objection to Descartes, and Descartes's official reply to Arnauld, are fleshed out metaphysically and epistemologically in anticipation of the third way, Descartes's theory of complete substances. Arnauld's objection embodies the view that real possibility is conceptually prior to conceivability. This view is questioned and contrasted with the thesis of the primality of conceivability over possibility, itself eventually rejected. Descartes's conception of complete substances emerges as provisionally victorious in its attempt to secure the real distinction, pending the discussion of non-generic essences in later chapters. This view combines the epistemological advantages of stressing the primacy of conceivability with the metaphysical constraints supplied by essence. The chapter concludes with a look at Kripke's modern conceivability arguments.
Keywords: conceivability, dualism, essence, possibility