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Re: [ontolog-forum] Ontology, Information Models and the 'Real World': C

To: "[ontolog-forum]" <ontolog-forum@xxxxxxxxxxxxxxxx>
From: "John F. Sowa" <sowa@xxxxxxxxxxx>
Date: Wed, 30 May 2007 21:54:00 -0400
Message-id: <465E2AB8.1030208@xxxxxxxxxxx>
Wacek, Ken, Pat, Ingvar, et al.,    (01)

I agree that one should use technical terms in a way that stays
fairly close to traditional usage.  But the tradition has a lot
of branches.  In some branches, a proposition is fairly close
to a sentence, but with the option of considering a restatement
in a different language to be "the same" proposition.    (02)

I take that to mean that a proposition is the language-independent
"meaning" or "intension" of a sentence, and that the truth value
is evaluated in terms of some "extension" or universe of discourse.
If somebody changes the extension or universe of discourse, then
the truth value may change.  But the intension remains fixed.    (03)

That interpretation is consistent with most 20th-century work
on modal and other kinds of intensional logics.  Montague, for
example, defined the intension of a sentence to be a function
that maps possible worlds to truth values.  Different possible
worlds are different extensions, but the function (intension)
remains fixed.    (04)

Although I prefer Dunn's semantics of laws and facts to a
Kripke-Montague version with possible worlds, Dunn's approach
produces exactly the same truth values for the same sentences.
That implies that the same sentence with the same intension
(proposition) may have different truth values in different
circumstances.  (I don't care whether anyone chooses to use
the terms 'possible worlds', 'universes of discourse', or
'contexts' for those circumstances.)    (05)

As Ingvar pointed out, Quine requires propositions to have
fixed truth values.  But that follows from the fact that he
does not allow different possible worlds or contexts.    (06)

Although I do not like the notion of possible world, I would
agree with the modal logicians that any theory of modal logic
should permit the same intension (proposition) to have different
truth values in different extensions (universes of discourse).    (07)

I also agree with Pat that the word 'context' has been used
in too many confused and confusing ways.  But I don't like
either of the following ways of talking:    (08)

KC>> In that sense, a change in context BECOMES a
 >> change in meaning of a proposition    (09)

PH> No, that is muddled. That is exactly what does NOT happen.
 > A proposition never changes its meaning. The SENTENCE
 > expresses different propositions.    (010)

I wouldn't say that a proposition changes its meaning
because I would prefer to say that a proposition *is* the
meaning of a sentence.  I also would not say that a sentence
whose indexicals were resolved to specific referents could
express two or more different propositions.    (011)

I'm sure that one can find logicians such as Quine who would
disagree with this interpretation.  But I believe that it is
consistent with those logicians who are more tolerant of modal
logic.  And since I want to represent modal sentences in NL,
I prefer to accommodate their usage (even though I use Dunn's
semantics rather than Kripke's).    (012)

John    (013)

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