Edward Erwin has recently argued against the thesis that the concepts a priori truth’ and ‘necessary truth’ are extensionally equivalent. This thesis consists of two logically independent claims: all a priori truths are necessary; and all necessary truths are a priori. Erwin leaves the first claim unchallenged and elects to devote his efforts exclusively to undermining the second. The brunt of his attack on the second claim rests on alleged unclarities in the concept of an a priori truth. He attempts (...) to show that the E.E.H. cannot be defended upon any plausible interpretation of this concept. Although I agree that the E.E.H., as stated above, is open to Erwin's objections, I shall argue that a slightly revised version of it can be defended against these objections. (shrink)

The main chapters of this thesis develop and defend a version of two-dimensional semantics that provides an account of Kripkean a posteriori necessity.