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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: Tue, 29 May 2007 08:17:59 -0400
Message-id: <465C19F7.2000009@xxxxxxxxxxx>
Wacek,    (01)

There is a difference between saying that all the referents
of a proposition are fully specified (i.e., no indexicals)
and saying that the proposition has the same truth value in
all contexts.    (02)

JFS>> If all such languages are able to express the "same" propositions
 >> (in whatever sense of "same" seems reasonable), then the simplest
 >> assumption is to assume that the "language-independent meaning"
 >> is converted to a context-independent form by assigning specific
 >> referents to the indexicals.    (03)

vQ> This is reasonable; I agree, and actually hoped for such an answer.
 > However, in your (fascinating) book on knowledge representation, you
 > write:
 > "
 > McCarthy (1993) introduced the predicate ist(c,p), which may be read
 > "the proposition p is true in the context c."
 > "
 > You do not seem to criticize this, though here propositions appear
 > to be context-dependent in their truth.    (04)

Since McCarthy was using a version of predicate calculus in which
there are no indexicals, the question of context dependence for
meaning does not arise.  But he definitely did want to talk about
propositions (or sentences) that had different truth values in
different contexts.    (05)

For example, consider the following sentence:    (06)

    "No roses are blue."    (07)

This sentence and its translations to other languages, natural
or artificial, have always been true.  However, some people
have taken a gene from petunias that encode the color blue
and inserted it into some roses.  They are now breeding blue
roses.    (08)

The meaning of that sentence has not changed in any way, but
because the world has changed, its truth value has changed.    (09)

vQ> In the above example from IKL [Dead Osama], it seems
 > that the truth of the proposition *is* taken to be
 > context-dependent, and that it includes an unresolved
 > indexical -- a temporal one.    (010)

The predicate isDead is a special case because people (and
other animals) don't normally switch back and forth between
a live state and a dead state.  But consider the following    (011)

    (isSleeping Osama)    (012)

There is nothing unusual about saying that the meaning of
this statement is context independent, but that its truth
may change from one context to another.    (013)

And by the way, I revised and extended that discussion from
Chapter 5 of my KR book in the following two papers:    (014)

    Laws, Facts, and Contexts    (015)

    Worlds, Models, and Descriptions    (016)

These models allow identical conceptual graphs g1 and g2 in
different contexts C1 and C2 to have all their referents bound
in some containing context C.  Yet the truth value of g1 in
context C1 can be different from the truth value of g2 in C2.    (017)

John    (018)

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