A priori and a posteriori
Separation

Aprioricity, analyticity and necessity have since been more clearly separated from each other. American philosopher Saul Kripke (1972), for example, provides strong arguments against this position, whereby he contends that there are necessary a posteriori truths. For example, the proposition that water is H O (if it is true): According to Kripke, this statement is both necessarily true, because water and H O are the same thing, they are identical in every possible world, and truths of identity are logically necessary; and a posteriori, because it is known only through empirical investigation. Following such considerations of Kripke and others (see Hilary Putnam), philosophers tend to distinguish the notion of aprioricity more clearly from that of necessity and analyticity.

Kripke's definitions of these terms diverge in subtle ways from Kant's. Taking these differences into account, Kripke's controversial analysis of naming as contingent and a priori would, according to Stephen Palmquist, best fit into Kant's epistemological framework by calling it "analytic a posteriori." Aaron Sloman presented a brief defence of Kant's three distinctions (analytic/synthetic, apriori/empirical and necessary/contingent), in that it did not assume "possible world semantics" for the third distinction, merely that some part of this world might have been different.

The relationship between aprioricity, necessity and analyticity is not easy to discern. Most philosophers at least seem to agree that while the various distinctions may overlap, the notions are clearly not identical: the a priori / a posteriori distinction is epistemological; the analytic/synthetic distinction is linguistic; and the necessary/contingent distinction is metaphysical.
combination:two_responses, oulipo:avoid_letter[e]