[FOM] Possible worlds

[Kenny Easwaran]

On 12/18/06, Harvey Friedman <friedman at math.ohio-state.edu> wrote:
> The notion of possibility being used in your example is an epistemic one,
> not an ontological or metaphysical one.
>
> I think that the computer science literature, rather than the philosophy
> literature, is what is most relevant. In the computer science literature,
> the non monotonic case is also treated, where things that were "known" are
> retracted. This makes especially good sense in database theory.

There is also a growing philosophical literature on epistemic modality
and the semantics of epistemic modal expressions.

The treatment by Andy Egan, John Hawthorne, and Brian Weatherson in
"Epistemic Modals in Context", and by John MacFarlane in "Epistemic
Modalities and Relative Truth" argues that epistemic modality is just
about compatibility with some set of knowledge.  (Their disagreement
is about which particular set of knowledge is relevant - the
speaker's, the hearer's, or others.)

Eric Swanson, in "Something 'Might' Might Mean" suggests that
epistemic modal claims like the one you mentioned don't even have
truth conditions, but instead are a way of giving advice on how to
assign one's partial beliefs.

Some of this literature makes use of "possible worlds"-style models of
information states, but in most cases I don't see why the worlds
shouldn't be thought of just as first-order structures rather than as
more robust actually-possible worlds.  David Chalmers and Frank
Jackson have been working on ways to try to characterize the relevant
notion of possible world, but I don't know if any of that work has
been published yet.

Kenny Easwaran