Apropos Williamson. The following question came up last year when
we discussed The Philosophy of Philosophy in Canberra. I
thought it had a sensible answer that we just couldn't figure out, but
then Dorothy Edgington raised the same question at the recent
phloxshop workshop in Berlin, and even though there were quite a few
Williamsonians present, there was no agreement on what the answer is,
and the proposals didn't sound very convincing.
The question is simply how, on Williamson's account, we can have
knowledge of substantial metaphysical necessities, e.g. of the fact
that gold necessarily has atomic number 79. Williamson explains that
when we counterfactually imagine gold having atomic number 78 (knowing
that it has number 79), we will "generate a contradiction", because we
hold "such constitutive facts [as atomic number] fixed" (p.164). But
the distinction between constitutive and not-constitutive facts can
hardly be analysed as the distinction between whatever we happen to
hold fixed and the rest, given Williamson's commitment to strong
mind-independence of metaphysical modality. So what justifies our
holding fixed the atomic number?
Carrie, Joe and Brit have recently commented on Williamson's proposal that modal knowledge is based on counterfactual knowledge. I share their suspicion, partly for the reasons Carrie mentions: the mere fact that statements about necessity and possibility are equivalent to counterfactuals doesn't tell us that the route to knowing the former proceeds via the latter. In fact, the assumption that we have a special cognitive faculty for knowing counterfactuals already seems odd to me. After all, we don't have special faculties for knowing indicatives or negations or conjunctions.
1. There is nowadays considerable evidence for the existence of pulsars. Still, it isn't incoherent to worry that the evidence might be misleading and pulsars don't exist after all. But it is incoherent to worry that pulsars might be the apple trees in my parents' garden. These apple trees aren't neutron stars, and they don't emit regular pulses of electromagnetic radiation, and things that don't do that don't deserve the name "pulsar".
2. Suppose we are convinced by van Inwagen's arguments that fictional characters are abstract entities created by authors and denoted by our fictional names. This suggests the following picture: Over and above our material universe there is a special realm of abstract fictional characters. Everytime an author writes a novel, new entities pop up in this fictional realm. There is no causal connection from the fictional realm to our world. But then how do we know about the fictional characters? How can we be sure for example that the creation of fictional characters is reliable? Couldn't it happen from time to time that a fictional character fails to be created? If so, perhaps Madame Bovary exists, but Sherlock Holmes doesn't. In which case it would be false (on the Kripke-van Inwagen account) that Sherlock Holmes was invented by Conan Doyle or that he is a widely known fictional character. Isn't our confidence in such assertions rather mysterious and irresponsible given that really we have no access at all to the fictional realm? At the very least, the exceptionless correspondence between what our authors do here on Earth and what happens in the fictional realm cries for explanation!
Brian Weatherson:
We know that positive conceivability is a good inductive guide to possibility. And we know negative conceivability is a good inductive guide to possibility.
What kind of induction is this? What we do know is that sometimes what seems conceivable on first sight later turns out to be incoherent (and thus inconceivable in the technical sense introduced by Dave Chalmers and deployed by Brian). We also know that this doesn't happen very often, and that it happens mainly when we consider rather complicated stories or hypotheses. So we have good inductive reason to assume that there is no hidden contradiction in, say, the hypothesis that there could be an apple in a basket. But this only supports the claim that prima facie conceivability is a good inductive guide to ideal conceivability.
If a statement p is impossible, then empirical information and a priori reasoning usually suffice to establish its impossibility. So if despite carrying out the relevant empirical investigations and a priori reasonings no impossibility shows up, this is a good reason to believe that p is possible. One might be tempted to say that our knowledge of possibility is always based on such a failure to detect the respective impossibility. This is what Bob Hale calls an asymmetric approach to modal epistemology. (See his "Knowledge of Possibility and of Necessity", Proceedings, 2003.)
Brute necessity is hard to accept, much harder than brute possibility. If someone claims that necessarily there are no purple cows, I expect an explanation. Perhaps he knows what kind of DNA is essential for cowhood and also that this kind of DNA can never produce purple beings, and he also believes that the laws of nature are necessary. This would make his claim understandable. But suppose he had no such explanation. Suppose in fact that we all know that only a minor mutation would be required to produce purple cows, a mutation perfectly compossible with the laws of nature. And still he claims that there could not be any purple cows. This would seem bizarre.
Here's a little question about David Chalmers' paper "Does Conceivability entail Possibility?". I'm interested in the relation between what Chalmers calls strong scrutability and what he just calls scrutability. In particular, I wonder if strong scrutability is really stronger than mere scrutability. This depends on a claim Chalmers makes in sections 10 and 11: that if there are inscrutable truths, it follows that some statements are epistemically possible (not ruled out a priori) but yet not really (primarily) possible. My question is: why does that follow?