There is but one totality of worlds; it is not a world; it could not have been different. (Lewis, Plurality, p.80)
If the totality of worlds could not have been different, then presumably no possible world could have failed to exist.
Then in particular, the actual world, @, could not have failed to exist.
So there is an actually existing thing, namely @, that could not have failed to exist.
Even worse, arguably @ has some of its parts essentially. So there are some actually existing things besides @ that could not have failed to exist.
One might even say that all worlds have all their parts essentially, simply because worlds do not exist at other worlds. Then it follows that no actually existing thing could have failed to exist.
Conservatism as a methodological principle says that we should prefer new theories that resemble our old theories. (I don't mean the principle that a new theory should be at least as good as its predecessors, nor the principle that it should explain the success and failures of its predecessors. Very non-conservative theories can do that.)
What is the status of conservatism? Is it a primitive rule telling us that even if we know that some revisionary theory is as good as a conservative one -- that both explain roughly the same data, make roughly the same predictions, are equally simple, etc. --, we should prefer the conservative theory? (An otherwise good theory according to which there are no birds, but only bird-halluzinations, say, just seems incredible, in particular if a more credible alternative is available.) In this case, conservatism would resemble the simplicity principle that tells us to always prefer the simpler of otherwise equal theories.
When I prepared my talk at Heidelberg, I noticed some errors and oddities in the paper I had written. There were also a few interesting points raised in the discussion which I wanted to address. So in Switzerland, I almost completely rewrote the paper. Here is the new version: "Emperors, dragons and other mathematicalia".
[Update 2004-12-31: I've corrected another mistake: condition (1) on singleton relations should say that they are injective functions, not just that they are functions.]
I'm back. The conference was good; and Switzerland was quiet, white and beautiful.
The mountain whose rather flat slope you can see in the foreground is called "Um Su". It is a mountain without a summit.
I'm on my way to the German-Italian philosophy conference in Heidelberg. After that, I'll spend some days in the Alps. I won't have internet access there. (Also, my computer didn't want to boot this morning. Hopefully it was just too cold.)
I've made the script driving the Lewis tracker available for download here. (I have a couple of further ideas and even half-finished pages for david-lewis.org, but they currently suffer from a lack of time and money. Suggestions about useful content are of course welcome.)
I keep wavering between two different uses of "analytical". This entry is meant to remind me of the difference and of why I should prefer the one over the other.
On the first use, a sentence is analytical if it has a universal A-intension. On the second, a sentence is analytical if one can't understand it unless one believes it (this is what I, unoriginally, proposed last year). The first is the better explication.
It consumes energy and emits electromagnetic radiation. It contains a small wire filament. It is widely used all over the world. It was invented by Heinrich Göbel in 1854, though Americans often attribute its invention to Thomas Edison. What is it?
The electrical light bulb, of course.
But hold on. Is there really something that satisfies these conditions? What kind of thing would this be? It can't be any particular light bulb, say, the one in my bathroom. For this light bulb is used only in my bathroom, not all over the world, and most Americans don't even know that it exists. Nor can it be any other particular material thing. Nor can it be a mental object, something like the idea of a light bulb: ideas don't contain small wire filaments. This alleged thing, the light bulb, is a very strange kind of object. It is not a light bulb (all light bulbs are concrete, particular light bulbs), but like all light bulbs it contains a wire filament, consumes energy and emits electromagnetic radiation. It is is located in time (as it didn't exist before 1854), but presumably not at any particular location in space.
I've been assigned some boring administrative work, but that's finished now, I hope. Here are some rough thoughts on indifference and Adam Elga's Dr. Evil paper (PDF).
There are many possible individuals whose mental state is subjectively indistinguishable from my current mental state insofar as they all share my current phenomenal experiences and my (real or quasi-) memories. Some of them inhabit worlds that are exactly as I believe the actual world is, and are located in that world exactly where I believe I am located in the actual world. Others occupy very different places in very different worlds: they are brains in vats or inhabitants of gruesome counterinductive worlds. How should I distribute my credence among all these possibilities?
Oops, last night I exceeded my webspace quota. Apologies for the failures and error messages that this caused all over the place. Please let me know if something is still not working.