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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 10:07:12 -0400
Message-id: <465D8510.3050800@xxxxxxxxxxx>
Ingvar,    (01)

My position and Pat's position are compatible and for the same
reasons:  we both have propositions, but we admit that their
truth values in different contexts can be different.    (02)

IJ> Implicitly, I take it, it then also introduces a new notion
 > of 'proposition-in-a-context' that ought not to be conflated
 > with the traditional philosophical and logical term 'proposition'.
 > A proposition-in-a-context can change truthvalue, a proposition
 > cannot.  Stated in this way, I have no objections.    (03)

You can add the qualifier "-in-a-context", if you like, but then
you also need to add the qualifier "-in-a-world" to accommodate
propositions in Kripke or Montague semantics.    (04)

Quine's position is consistent with his anti-modal stance:    (05)

WVOQ> "The newly remarked purpose of propositions as surrogate
 > truth vehicles demands that propositions resist variation in
 > truth value, ..."    (06)

If you only allow one world or context, then I would agree that
a proposition would be restricted to a single truth value.    (07)

But in modal logics (with a semantics based on either Kripke's
possible worlds or Dunn's laws and facts), the same proposition
with the same referents can have different truth values in
different worlds.    (08)

A question does arise about what "same referents" means, and
that is why I quoted Whitehead's point about the fallibility
of reference.  But various theories of possible worlds have
rigid designators that allow names in different worlds to
designate the "same" individual.    (09)

As I said, I have serious concerns about the ontology of
possible worlds, but I am happy with a model theory that
has contexts that can be interpreted either way:    (010)

  - Kripke style:  Possible worlds with rigid designators.    (011)

  - Dunn style:  Collections of propositions that describe
    possible alternatives and with the equivalent of rigid
    designators that can fix the referents of some or all
    of the identifiers in a proposition.    (012)

I outlined a version of such a model theory in my laws.htm
paper, but there are many other versions of modal models
with similar properties.    (013)

In short, I would agree that if there is only one world or
context (as in Quine's logics), then a given proposition
cannot have more than one truth value.  But any version of
modal logic with a semantics of multiple worlds or contexts
must admit that a given proposition may have different truth
values in different worlds or contexts.    (014)

John    (015)

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