Here is a short paper version of my GAP.6 talk "Modal metaphysics and conceptual metaphysics", to appear in the GAP.6 proceedings. It has a lot less formulas than the talk.
I distinguish two metaphysical projects: modal metaphysics and conceptual metaphysics. I show that the two projects really are distinct, and that Frank Jackson's argument for the opposite conclusion doesn't work. Then I have a closer look at how the projects come apart, and suggest that when they do, the modal project always becomes metaphysically uninteresting. Thus the term "metaphysical modality" is a misnomer: metaphysical entailment only matters for metaphysics insofar as it coincides with conceptual entailment.
I suppose I should say a little more on what I call "modal back-reference", and on the sense in which what a sentence expresses can be conceptually independent of how things are in the actual world: doesn't what a sentence express always depend on what the sentence means? Unfortunately, I don't have a simple and uncontroversial answer to that, so I just ignored this point. Hopefully no-one will notice.
I've fixed the bug where sometimes nodes in the displayed tree overlapped. I also made the proof search faster. Now Pelletier 34 is proved in only a few minutes! (Warning: the tree is huge, and might crash your browser.)
Brian argues that our intuitions about whether an action C causes somebody's continued survival is linked to the applicability of causative notions like "opening", "closing", "protecting", "threatening": if C inadvertently causes the survivor to be threatened but at the same time protects him from the threat, we are more inclined to count C as causing the survival than if C threatens the surviver but at the same time inadvertently causes him to be protected.
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.
I remember the years when this blog, because I wrote the software myself, received zero comment spam. Now it's about 1500 spam comments a day, and some have recently made it through. So I've stepped up the measures again. Every submitted comment now gets assigned a score based on 1) whether the POST request matches up with a previous GET request of the form page by the same client, 2) whether the client has fetched an image embedded in the form, 3) whether the client supports JavaScript, 4) whether the client supports cookies, 5) whether it took more than 5 seconds and less than 24 hours to fill in the form, 6) whether all form fields (including hidden ones) are submitted, 7) whether several randomly inserted form fields that are turned invisible with CSS have been left blank, 8) whether the submitted text doesn't contain spammy words, and 9) whether the same IP has not recently sent me something with a high spam score. If the score is high, you get a warning; if it is very high, you get blacklisted for 10 minutes and sent into a (mild) tarpit. I hope this combination will trap all the spam while not blocking any legitimate users who have merely turned off, say, images and JavaScript. I've tried it with Lynx and it worked fine. Let me know if you run into any problems.
I've fixed a tricky bug in my tableau prover that messed up the displayed proof in cases where the expansions of an alpha or beta formula are different, but their negation normal form is the same (example). Thanks to Christoph Pfisterer for pointing out this problem to me.
I've also begun working on a new version that allows for easy switching and editing the algorithm, so that one can use different logics and try out different precedence rules etc. At the current rate of development, this version will probably be finished around 2012.
Lewis once proposed that a 'might' counterfactual ![$m[1]](/texer/images/?format=gif&fontsize=12pt&tex=A+%5CDiamondright+C)
("if A had been the case, C might have been the case") is true iff ![$m[1]](/texer/images/?format=gif&fontsize=12pt&tex=%5Cneg%28A+%5Cboxright+%5Cneg+C%29)
is true. This is sometimes used in defense of controversial philosophical claims, like in Al Hájek's "Most Counterfactuals are False" and in Boris Kment's "Counterfactuals and Explanation". But at least in some cases, the analysis doesn't seem right.
Just when I thought all viruses are specific, I caught an 'unspecific virus' last weekend -- at least that's what the doctors at the hospital identified it as. So I've been knocked out for about a week, but now I'm back with an exciting new theory of modality.
The theory is simple. It says that everything is possible. Pace Kripke, there are possible worlds where Queen Elizabeth is a poached egg and where Hesperus isn't Phosphorus. And pace almost everybody else, there are possible worlds where squares are round, bachelors married and where Hesperus isn't even self-identical.
This appears to be a problem for pure epistemic accounts of indicative conditionals (a la Weatherson and Chalmers), on which "if A then B" is true iff the [epistemically] closest worlds verifying A also verify B.
The match cannot be played if it rains; either it has to be postponed or canceled. Which of these will happen is regulated by the rule book, but nobody has looked up the relevant passages so far. All we know is that exactly one of these two conditionals is in the rule book, and therefore true, and the other false:
