Something I often worry about is what sorts of appeals to “the linguists” or “linguistic research” are legitimate, and which are not. Here is a particular case, which I haven’t really thought about in a serious way yet, but which I have run into in some of my work lately on expressivism. (More likely than not that I’m retreading stuff that Seth Yalcin or Eric Swanson has written about before, so I hereby cancel any implication of originality.)
I think there’s a pretty wide consensus among linguists on what we might call a specific, inflationary notion of assertion. Generally speaking, inflationary notions of assertion involve an answer to the question what does an assertion that p typically communicate? that goes beyond merely that p. For instance, on one inflationary notion of assertion (Stalnaker’s), if someone asserts that it might by raining, they propose the proposition that it might be raining (a set of possible worlds where it might be raining) for addition to the Common Ground. On a deflationary notion of assertion, the question what does an assertion that p typically communicate? is answered simply by that p. The deflationary notion is, as you’d expect, weaker than the inflationary notion: nonfactualists and factualists about epistemic modality alike will agree that epistemic modals are apt for assertion in the former sense, but may disagree about whether they are apt for assertion, on whatever inflationary notion of assertion is your favorite. (I could be more rigorous about all of this setup, but I won’t.)
Okay, so here’s the sort of appeal to linguists that I’m interested in. (Note: I think there’s something a bit glib about it, although I’m not quite sure why.) If there’s anything like a consensus view about how to model assertion among linguists (I think it’s fair to say there is), it’s something rather close to Stalnaker’s. But actually I can make the argument I want with something weaker. I think there’s a pretty wide consensus among linguists about a certain kind of inflationary notion of assertion: the contents of felicitous assertions typically (modulo certain puzzling kinds of sentences, like potentially informative necessary truths) characterize (although they aren’t necessarily identical to) contingent possible-worlds propositions.
Now consider a nonfactualist about some kind of language K (epistemic modals, normative claims, whatever). According to the nonfactualist about K, a sentence of type K does not have a proposition as its semantic value; it doesn’t function, as a matter of its semantics, to represent the world as being one way or another. So such sentences, if they characterize possible-worlds propositions at all, can characterize only the entire universe (or the empty set). According to the linguists’ consensus, inflationary notion of assertion, something characterizing this sort of possible-worlds proposition is typically not assertable (unless it is one of the puzzling kinds of sentences, which, we’ll suppose language of type K is typically not). We can trust the linguists about which inflationary notion of assertion is best suited to modeling the ordinary exchange of information in conversation. So, for the nonfactualist about K, sentences of kind K are assertable only in a deflationary sense (or some inflationary sense that is not of legitimate empirical interest).
There’s potential for some pretty big philosophical payoff here. This sort of argument seems to rule out, right off the bat, certain forms of nonfactualist expressivism about normative language: for instance, those on which normative and non-normative declaratives express assertions in the very same (inflationary) sense. There’s also a way to leverage these sorts of considerations in constructing a (defeasible) argument against nonfactualism about any kind of declarative sentence. Linguists tend to agree that declarative sentences are conventionally apt for assertion (in, I’d presume, the aforementioned inflationary sense). So we would expect the sorts of declaratives we see people using with regularity in communication to conventionally characterize non-trivial possible-worlds propositions. But it is, at first glance, a bit hard to see how they should be able to do that, for a nonfactualist about any sort of declarative. (This argument’s not strictly valid, but I think there are plausible ways of making it so.)
These arguments, as I said, seem a bit glib to me, although I’m not quite sure why. There’s something just off about this way to deferring to the linguists — I’m just not sure what it is.