Online Papers - Brian Weatherson

David Lewis 76
to there being at least one world. As (Melia, 1992, 192) points out though, the inhabitants
of those worlds include all kinds of things not found in, or reducible to,
fundamental physics. They include spirits, gods, trolls and every other consistent
beast imaginable. So at least when it came to what there is, as opposed to what there
actually is, Lewis’s ontology was rather expansionist.
For all that, Lewis’s default attitude was to accept that much of our commonsense
thinking about the nomic, the intentional and the normative was correct, and
that this was perfectly compatible with this world containing nothing more than is
found in science, indeed than is found in fundamental physics.
Compatibilists should solve what Frank Jackson calls ‘the location problem’ (Jackson
1998). If you think that there are, say, beliefs, and you think that having beliefs in
one’s metaphysics doesn’t commit you to having anything in your ontology beyond
fundamental physics, then you should, as Jackson puts it, be able to locate beliefs
in the world described by fundamental physics. More generally, for whatever you
accept, you should be able to locate it in the picture of the world you accept.
This was certainly the methodology that Lewis accepted. And since he thought
that so much of our common sense worldview was compatible with fundamental
physics, he had many versions of the location problem to solve. One way to go
about this would be to find exactly what the correct scientific theory is, and locate all
the relevant properties in that picture. But this method has some shortcomings. For
one thing, it might mean having to throw out your metaphysical work whenever the
scientific theories change. For another, it means having your metaphysics caught up
in debates about the best scientific theories, and about their interpretation. So Lewis
took a somewhat different approach.
What Lewis’s defence of Humean supervenience gives us is a recipe for locating
the nomic, intentional and normative properties in a physical world. And it is a
recipe that uses remarkably few ingredients; just intrinsic properties of point-sized
objects, and spatio-temporal relations. It is likely that ideal physics will have more
in it than that. For instance, it might have entanglement relations, as are needed
to explain Bell’s inequality. But it is unlikely to have less. And the more there is
in fundamental physics, the easier it is to solve the location problem, because the
would-be locator has more resources to work with.
The upshot of all this is that a philosophical defence of Humean supervenience,
especially a defence like Lewis’s that shows us explicitly how to locate various folk
properties in classical physics, is likely to show us how to locate those properties in
more up-to-date physics. So Lewis’s defence of Humean supervenience then generalises
into a defence of the compatibility of large swathes of folk theory with ideal
physics. And the defence is consistent with the realist principle that truth supervenes
on being, and with the Humean denial of necessary connections between distinct
existences. And that, quite clearly, is a philosophically interesting project.
6 Modal Realism
This entry has been stressing Lewis’s many and diverse contributions to philosophy.
But there is one thesis with which he is associated above all others: modal realism.