More on privacy, apriority, and two-dimensionalism
Here are, very quickly, some more thoughts on the matters I talked about here and there, inspired by another discussion with Christian.
You don't have to know much about plutonium to be a competent member of our linguistic community. One thing you have to know is that plutonium is the stuff called 'plutonium' in our community. Maybe that alone suffices. Of course, if noone knew more about plutonium than this, the meaning of 'plutonium' would be quite undetermined. To fix the meaning, it would suffice if a few persons, the 'plutonium experts', knew in addition that this element (where each of the experts points at some heap of plutonium) is plutonium.
I take it that Kripke and Putnam correctly reminded us that something like this might well be true. From which it follows that if analytical truths are truths that every competent speaker can come to know just by reflecting on the meaning of his words, there might not be much analytical truth about plutonium. Likewise, there might not be much that can be known a priori about it, no matter how apriority is defined.
All this is independent of modal intuitions, so two-dimensionalism won't help to secure substantial a priori or analytical truths.
Nevertheless, two-dimensionalism still works, on both the individual and public level. For example, it still explains why in some sense we wouldn't speak a different language if physicists had found out that water is XYZ. And it is still the best way to account for all kinds of context-dependence.
Moreover, we can still use something like conceptual analysis to do reductive metaphysics. In the plutonium case, plutonium is whatever substance roughly satisfies the description: 'stuff that everyone calls plutonium and that the experts are pointing at' (where maybe the first clause is redundant).
This also shows that descriptivism really can survive. It doesn't survive by opposing the Kripke/Putnam account, but rather by incorporating it completely as a special case. By including clauses like 'roughly', descriptivism can actually handle some cases of 'non-descriptive' reference-fixing better than the original Kripke/Putnam account, for instance the madagaskar, phlogiston, vulcan and jade cases.