This summer I'm trying to get a little bit up to speed on modality issues by doing an independent study with some students.* I've started looking ahead to Williamson's recent magnum opus and this little bit of the preface weirded me out:
Since cosmological theories in physics are naturally understood as embodying no restriction of their purview to exclude Lewis's multiple spatiotemporal systems, many of which are supposed to violate their laws, his cosmology is inconsistent with physicists', and so in competition with them as a theory of total spatiotemporal reality. On such matters, physicists may be felt to speak with more authority than metaphysicians. The effect of Lewis's influential and ingenious system-building was to keep centre stage a view that imposed Quine's puritan standards on modality long after Quine's own eliminativist application of those standards have been marginalized (Williamson 2013, xii)
I don't get this at all.
The connection between Lewisian Genuine Realism and Quine's eliminativism is a promissory note that I assume he'll cash in later, but the first bit just makes no sense to me. In On the Plurality of Worlds, Lewis explicitly says that the nomologically possible worlds will be a subset of all possible worlds and he discusses physically impossible forms of space time in this context. He has to do this, since possible worlds are individuated by the space-time which each world shares with itself. But nowhere does he make claims about which class of worlds will be the nomologically possible ones.
I realize that commitment to physical impossibilia might be bad for other reasons (doesn't Sydney Shoemaker argue to this conclusion?), but even so why think that it's within the physicists purview to rule all of them out? I think I'm missing something.
[Notes:
*If I were playing the original Lodge humiliation game (rather than the philosophical versions we devised here), I would have to name Lewis' Possible Worlds. This summer we're reading first that book, then John Divers', and finally Williamson's, and then in spring I'll teach Stalnaker's new one. Next summer I hope to be able to tackle some of the new stuff about modal realism without possible worlds as well as delve further into all things Barcanium.**
**My intuition is that the Barcan formulas are trivially true because the existential quantifier does not ontologically commit. That is, it's no big deal to say that it's possible that something is a unicorn entails that something is such that it's possible that that thing is a unicorn, as long as "something" (expressed by the existential quantifier) doesn't carry ontological commitment.*** This probably doesn't get you very much though: (1) because you'd still need to characterize an existence predicate such that analogues aren't derivable, (2) if I understand right, Priest blocks the Barcan formula for his existential quantifier even though it doesn't commit for him, and (3) if I understand right, Williamson's book is largely a defense of the Barcan formulas while accepting that the existential quantifier carries ontological commitment with it. So the "people smarter than me probalby have good reasons for disagreeing" inference is making me think I'm probably wrong. Hopefully I'll get clear on Williamson this summer and Priest next summer. I also need to (1) see if anyone else has the same intution I do, (2) get a better logician than me to reformulate Kripke's proof theoretic block of the Barcans within a normalizable modal system (see here for K and here for T, S4, and S5) so I can be clearer about what's at stake.
***There are decent linguistic reasons to think it doesn't and in one's formal treatment to treat the existential quantifier (and indeed proper names) likewise. But to take these as relevant presupposes a lot about the role of "canonical notation" in metaphysics. I think Priest gets this stuff correct in his critique of Quine, but it's worth thinking about more deeply.]
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