RE: modal logic
Dear John,
I re-read the stuff you mention below. It seems to me that it is not so much
that you object to Possible Worlds (the people you quote build on the basic
idea) but rather that the concept of possible worlds alone leaves too much
to the imagination. Certainly what you quote seems to add something useful
to the bare concept.
Regards
Matthew
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Matthew West
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> -----Original Message-----
> From: John F. Sowa [mailto:sowa@west.poly.edu]
> Sent: 04 July 2000 15:02
> To: Nicola.Guarino@ladseb.pd.cnr.it; apease@teknowledge.com;
> cmenzel@tamu.edu
> Cc: onto-std@KSL.Stanford.EDU; standard-upper-ontology@ieee.org
> Subject: Re: modal logic
>
>
>
> Chris, Nicola, et al.,
>
> >... I agree what you seem to
> >suggest, that the minimal modal logic S5 is adequate for most cases.
>
> S5 is not minimal; it is maximal. S5 is one of the strongest of all
> versions of modal logic, and in an earlier note, I cited the example
> to show that S4 is closer to the usual policy of database
> administrators.
>
> >... Grasping the *meaning* of a certain term (i.e.,
> >its "intension") implies being able to competently use that term in
> >different worlds. That's why ontologies cannot avoid some notion of
> >possible worlds.
>
> This gets back to the other point I was making. Possible
> worlds themselves
> are ontologically dubious, and some very competent
> philosophers, such as
> Quine, have never accepted them. In Ch 5 of my KR book, I summarized
> those objections to possible worlds, and used an equivalent semantics
> by Michael Dunn (1973), which replaces the notion of possible world
> with a pair (L,F) of propositions called laws and facts. Dunn showed
> that Kripke's accessibility relation can be analyzed as restrictions
> on the permissible variations of laws and facts as you move from one
> world to another. All of Kripke's semantics follows from Dunn's
> approach, but the philosophical and computational foundations are
> much clearer and more explicit.
>
> >>S5 is the most popular, but some philosophers (notably
> Nathan Salmon)
> >>have argued that it is too strong, especially with regard
> to the modal
> >>properties of artifacts.
> >
> >Have you got a pointer?
>
> See Ch 5 of my KR book.
>
> John
>