Published online by Cambridge University Press: 01 January 2020
Edward Erwin has recently argued against the thesis that the concepts a priori truth’ and ‘necessary truth’ are extensionally equivalent. (Following Erwin, I shall refer to this thesis as the ‘Extensional Equivalence Hypothesis’ or, for short, E. E. H.) This thesis consists of two logically independent claims: (1) all a priori truths are necessary; and (2) 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.
2 I shall not consider here Saul Kripke's well known objections to both parts of the E.E.H. They are discussed in my “Kripke on the A Priori and the Necessary,” Analysis 37 (1977), pp. 152-59.
3 Erwin, p. 594.
4 Roderick M. Chisholm offers the following definition of “h is a priori” which is not dependent on contingent features of the world: “It is possible that there is someone for whom h is a priori.” See Theory of Knowledge, 2nd ed. (Englewood Cliffs: Prentice-Hall, Inc., 1977), p. 45.Google Scholar The problem with such a definition, as Erwin points out, is that it would make virtually all contingent truths a priori truths. Panayot Butchvarov also argues, “Is there an obvious contradiction in the supposition that I may derive such knowledge [that there is a typewriter before me now] with formal validity solely from premises of which I have primary a priori knowledge?” See The Concept of Knowledge (Evanston: Northwestern University Press, 1970), p. 103.Google Scholar
5 Erwin, p. 598.
6 Ibid., p. 599.
7 One possible account of nonexperiential evidence is defended in my “Conceivability and Possibility,” Ratio 17 (1975), pp. 118-21. For a more complete discussion of the problem of defining a priori knowledge, see my “The Definition of A Priori Knowledge,” Philosophy and Phenomenological Research 38 (1977), pp. 220-24.CrossRefGoogle Scholar
8 For two radically different approaches to the problem of answering sceptical challenges to a priori knowledge, see Butchvarow, pp. 76-88 and Chisholm, pp. 48-50.