But (as I noted in a subsequent comment) that just assumes that the defenders of analyticity might see the a priori as unacceptably metaphysical where analyticity is not. As it turns out, Hacker at least does not. I'll get to all that in a minute. Let me first give a quick and dirty characterization of four similar concepts, not worrying for the moment about whether any one of them can be collapsed into any of the others, or whether there really are any such things.
1. Tautologies are "truths of logic": P or not-P (in classical logic).
2. Analytic sentences are "truths (by virtue) of meaning": That bachelor over there is unmarried.
3. Truths are known a priori when we don't have to go out and look, but can confirm them from the proverbial armchair.
4. Truths are necessary when it is impossible for them to be false (they're "true in all possible worlds").
If you like these concepts, you can supply your own examples for the last two. (The SEP article on "A Priori Justification and Knowledge" has as an example of a necessary proposition this one: "all brothers are male," which is not one I would have chosen if I were trying to distinguish necessity from analyticity). Anyways, my point is that however the categories do or do not overlap, the characterization of each has its own typical angle: tautologies have to do with logic, analyticity with meaning, a priority with knowledge (and justification), necessity with ontology (or modality, or in any case metaphysics).
A lot of us want, in some sense or other, to rule out "metaphysics" as nonsense, e.g. a) Ryle, Hacker, etc.; b) Wittgenstein (early and late, on most interpretations); and c) some but not all naturalists. So necessity (or, redundantly, "metaphysical necessity") looks fishy to us. But (as I started to talk about before) in order to combat metaphysics (including but not limited to "necessity"), some of us think we need to hold on to analyticity – a concept which deals, the thought goes, not with the world (i.e., on the other side, qua the object of a "metaphysical" statement, of the "bounds of sense"), but with meaning (which is safely on "this" side). Or so I read Grice & Strawson (I'm trying not to make a straw man here!). For G & S, then, analyticity is both unobjectionable and
Where does that leave the a priori? If we assimilate it to necessity (on the one side), then it's a metaphysical notion, worthy of dismissal; and if analyticity is the "least metaphysical" of the three (on this quick and dirty characterization), then if Quine's attack on analyticity goes through, it seems that a fortiori (so to speak) the others go as well. But for "analysis" to be possible, G & S believe, there need to be such things as "analytic" truths. So again, my off-the-cuff suggestion was that if we drew the line between analyticity (needed for the method of "analysis") and the a priori, we could use the former to dismiss the latter (along with the more overtly metaphysical notion of necessity).
But Hacker at least is clear that he does not want to do this. For Hacker, the a priori is the central concept he wants to defend: not as a possibly unacceptably metaphysical subject (i.e. object) of philosophical speculation, but as its constitutive method. It is this and this alone which distinguishes philosophy from empirical inquiry. I should have realized this, as the notion is (as in the SEP article) characteristically applied to the manner in which knowledge is acquired rather than its (semantic) form or (ontological) object, and the main contention of the "conceptual analysis" folks is that, again, philosophy is a matter of the clarification of our concepts as specifically opposed to empirical inquiry; so of course they want to defend the a priori as well as analyticity. (My excuse is that I didn't want to assume the naturalist characterization of the a priori (i.e. as hopelessly unempirical) from the beginning, even, or perhaps especially, because I too am not too keen on the notion, if for somewhat different reasons.)
For a interesting account of Hacker's attitude toward Quine, I recommend his paper "Passing By the Naturalistic Turn: On Quine's Cul-de-sac" (available on his website). The main target is Quine's "naturalized epistemology" (so some of what Hacker says is perfectly congenial), and in attacking it Hacker commits himself
There has been a naturalistic turn away from the a priori methods of traditional philosophy to a conception of philosophy as continuous with natural science.and ends:
This imaginary science [naturalized epistemology] is no substitute for epistemology – it is a philosophical cul-de-sac. It could shed no light on the nature of knowledge, its possible extent, its categorially distinct kinds, its relation to belief and justification, and its forms of certainty. [...] For philosophy is neither continuous with existing science, nor continuous with an imaginary future science. Whatever the post-Quinean status of analyticity may be, the status of philosophy as an a priori conceptual discipline concerned with the elucidation of our conceptual scheme and the resolution of conceptual confusions is in no way affected by Quine's philosophy.Snap! That last sentence answers our (my) question about priorities (no pun intended) pretty clearly, I'd say. Let's come back to this article; it's got a nice mix of