[Alta-Logic] Logic and Category Theory Group: Talk on Oct. 1st

[ggpayett at ucalgary.ca]

Title: Worlds and Times

Date: October 1, 2008 (Wednesday)

Room: ICT 616

Time: 1pm--2pm

Speaker: Gillman Payette (Philosophy)

Abstract:

The Diodorian account of alethic modality runs something like this: P is
possible, if P is now true, or will be true. We can add to this definition
that P has been true since if it has been the case that P, then P had
better be possible. But this collapses what is possible to what merely
has, is or will be. That seems deterministic, and it seems to miss the
idea that there are things that are possible, but not actual.

Current modal logic which is done with possible world semantics does match
our intuitions, but it simply says that there is a relation R on the set
of possible worlds which gives us the alternative, accessible or
relatively possible, possible worlds to the actual. But what is this
relation R? The question is not whether this relation is transitive,
symmetric, etc., but what it is.

There is something that the Diodorian account gets right: the before/after
relation is something that we can make sense of. But if we use worlds and
times, we can give an account of the semantics of various uses of
'possible' that defines R in terms of before/after and matches our
intuitions. In this talk I will explain how to do this, and explain
possible world semantics. This is joint work done with Peter Schotch at
Dalhousie University.