I clicked through to David Chalmers's powerpoint slides on Ontological Indeterminacy yesterday, wondering if I might get a discussion of ontic vagueness. In fact I found something else equally interesting: a discussion of 'deflationary' (=, roughly, Carnapian) views about certain existential questions.
I have a few comments (though NB I have not heard the full talk, so maybe some of these points are addressed there):
1. I'm not sure whether the kind of 'relativism' Chalmers describes should count as deflationary. To say that there are many equally good answers to a question (which I think is the core of the proposed 'relativism') is prima facie different from saying that there is *no* substantial answer to the question (deflationism). To get the latter from the former we seem to need to assume that relativism about answers to a question is incompatible with the thought that the question and its answers are metaphysically substantial.
2. I think substantial ontological existence claims can be what Chalmers calls 'lightweight', i.e. a priori knowable or analytic or something in that area. Which is to say, in effect, that I don't think 'lightweight' (a priori knowable) existential claims need be genuinely lightweight. The envisaged connection between 'lightweightness' and real , metaphysical, lightweightness is, I guess, supposed to be effected by the thought that a priori reflection can only address what Carnap would call 'internal' questions, while genuinely heavyweight ontological questions must be 'external'. But personally (for what it's worth), I think concept-led a priori reflection might well lead to knowledge of substantial conclusions, including existential conclusions. Once we acknowledge that concepts can be grounded - i.e. sensitive to the way the world is in such a way as to make them good epistemic guides to reality - we can think (in Carnapian terms) of frameworks as being selected on more-than-pragmatic grounds, that is, selected for their fit with the world. And then there is no reason to doubt that a priori reflection on concepts within a framework can give us epistemically respectable answers to (what Carnap would have called) external questions.