The metaphysical and semantical ideas Saul Kripke advanced in the early 1970s, in Naming and Necessity and “Identity and Necessity,” have found wide acceptance among philosophers. But what is perhaps the most intriguing application he made of these ideas was in his discussion of the mind/body problem, where his arguments and conclusions are widely regarded as Cartesian in spirit; and here many fewer have been convinced. Those who accept the central ideas of his philosophy, but also accept materialist or physicalist views of the sort Kripke uses these ideas to attack, face the challenge of showing that these are not, as he forcefully argued, incompatible.