Re: SUO: Re: RE: Logic and Ontology
Chris,
I believe that we agree on the issues, and the only disagreement
is what terms to use to describe them.
CP> Sorry to be so picky. I agree with you that you have to be careful
> in picking your domain, otherwise - as you say - you get a distinction
> between intension and extension. But, I believe, David Lewis's point
> (in Plurality of Worlds et al) was that by picking the right kind of
> domain (including possible worlds) that the distinction between (some
> forms of) intension and extension collapsed. In other words, this can
> deal with "the case of different engineers discussing different design
> options for an airplane whose design is still unspecified" - which is
> home territory for Matthew - as a 'real' engineer.
In fact, some Montague defines the intension of a property P as a
function that applies to possible worlds. For each world w, the
intension of P gives you the set of all x's for which P(x) is true.
But the whole issue of possble worlds gets very slippery, since the
selection of worlds depends on whatever mode of modality you're talking
about. For physical necessity, the possible worlds are those that have
the same physical laws as our universe. For deontic modalities (i.e.,
obligation and permission), the possible worlds get even more slippery,
since people don't always do what's obligatory and they often do things
that are not permissible.
CP> But, as I said in the last email, I do agree with you about the
> differences between the use of property and set.
That was the main point I was trying to get across.
John