Let logicalism ("logicism" was already taken) be the claim that all truths supervene upon purely logical truths, where a purely logical truth is a truth that contains only logical terms, including terms from second order modal logic.
Logicalism immediately follows from this purely logical truth ('[]' is the box, 'ACT' the actually operator):
p <-> []((x)(F)(Fx <-> ACT(Fx)) -> p)
While all truths therefore supervene upon the purely logical truths, not all truths are a priori deducible from the purely logical truths. For instance, that water covers most of the earth isn't. So we have a counterexample to the claim that whenever all truths supervene on the F-truths, then all truths are a priori deducible from the F-truths.
Serious Metaphysics, in Jackson's sense, tries to identify a limited set of truths (i.e. true sentences) that entail (i.e. strictly imply) all truths. So what about
*) Everything is just as it actually is?
((p)(p <-> actually p), or (x)(F)(Fx <-> actually Fx))
(*) is true. It entails all other truths: whenever S is true, then so is "necessarily, if (*) then S". And it is fairly simple and economic: for instance, it doesn't contain macrophysical or phenomenal terms. Still, it's not serious metaphysics. What's wrong?
Apropos conceptual differences, Lewis didn't seem to care much about whether his
analyses exactly matched other people's semantic intuitions:
In "Veridical Halluzination and Prosthetic Vision", he claims that
prosthetic vision is properly called "seeing". He continues:
If you insist that "strictly speaking", prosthetic vision isn't really
seeing, then I'm prepared to concede you this much. Often we do leave
semantic questions unsettled when we have no practical need to settle
them. Perhaps this is such a case, and you are resolving a genuine
indeterminacy in the way you prefer. But if you are within your
rights, so, I insist, am I. I do not really think my favoured usage is
at all idiosyncratic. But it scarcely matters: I would like to
understand it whether it is idiosyncratic or not. (p.280 in Papers
II)
Another example: In Convention, he suggests that a regularity to dress in a particular way doesn't count as conventional if many people conforming to the regularity want others not to conform (so that they can poke fun at them). Realizing that this classification isn't obvious he notes:
If the reader disagrees, I can only remind him that I did not
undertake to analyze anyone's concept of convention but mine. (p.47)
He speaks of reminding the reader because he had already mentioned in the introduction that there might be no clear common concept of
convention. But, he adds, "what I call convention is an important
phenomenon under any name" (p.3).
In case anyone's interested, here is the preliminary study guide for my Wissenschaftstheorie course (postscript file, German). I've decided to spend a little time on constructivism and relativism because there's a parallel course on sociology of science, and at least in Germany it is common sociological practice to talk as if constructivism and relativism were true. (My principle of charity demands not to take this talk literally. It usually makes sense if one substitutes "theory" for "reality" and "belief" for "truth".)
On rereading Brian's counterexamples paper, I'm not so sure anymore I understand him correctly: Are the semantic values of predicates that are supposed to be fairly natural (unions of ranges of) C-intensions or (unions of ranges of) A-intensions? Philosophical analyses usually spell out A-intensions: they tell us that pain is what occupies the pain role, or that water is the watery stuff, not that pain is C-fiber firing and water H2O. So if the naturalness of semantic values speaks in favour of simple analyses, it should be naturalness of A-intensions. On the other hand, the fish example makes more sense if it is understood as talking about C-intensions (which would also match a suggestion sometimes made by Jackson, e.g. on p.95 of "From H2O to water", that we might analyse "water" as something like "the most natural kind roughly meeting such and such conditions"). The A-intension of "fish" presumably isn't all too natural, among other things it contains whales at worlds where the fishy animals of our acquaintance are mostly whales.
A few more comments on why I think the setup of Weinberg, Nichols and Stich's experiments on intuitions is unfortunate. The problem seems particularly obvious in the experiments on semantic intuitions reported by Machery, Mallon, Nichols and Stich, but I think it carries over to many (though perhaps not all) of the experiments of Weinberg, Nichals and Stich. Here is one of the questions Machery, Mallon, Nichols and Stich asked:
I don't understand what's so bad about admitting that people may use and understand the same words in slightly different ways.
Suppose there is a community of Martians who have a word for true
justified belief, but no word for knowledge. When these Martians learn
English, they might at first take "knowledge" to be synonymous with
their word: the difference hardly shows up in ordinary contexts. So when they use "knowledge", they mean true justified belief.
Eliezer Yudkowsky, in his Intuitive Explanation of Bayesian Reasoning, argues that it is irrational to justify the belief that if a biological war will break out it won't wipe out humanity by pointing out that one is an optimist:
p(you are currently an optimist | biological war occurs within ten years and wipes out humanity) =
p(you are currently an optimist | biological war occurs within ten years and does not wipe out humanity)
I'm preparing an introductory course on Wissenschaftstheorie that I'm supposed to teach next semester in the institute of library science. Unfortunately, the textbooks currently available in German are not nearly as good as many English ones.
Another (related) problem is that I'm not sure what Wissenschaftstheorie actually is. Well, I believe it is roughly the same as philosophy of science. But looking through German textbooks and the course guide of my predecessor, apparently some people think it also includes some or all of history and sociology of science, general epistemology, methodology, logic, philosophy of language, and stuff like hermeneutics and dialectics (whatever that is). I guess I'll stick to philosophy of science, even if that means using old textbooks by Carnap and Hempel.
The new tree prover has now replaced the old one at /logik/trees. I'm still grateful for all kinds of feedback, even if it's just letting me know that it works on your machine. Unlike the old version, which has retired to /logik/oldtrees/, the new one certainly doesn't work any more with Internet Explorer on the Mac and Netscape 4. If you're still using these browsers, you should really consider switching to Mozilla (or, on MacOS Classic, WaMCom).