>John F. Sowa wrote:
>
>> If we consider a proposition to be the "language-independent meaning"
>> of a sentence, then it should also be context independent as well.
>>
>> That point follows from the fact that different languages have
>> different means for representing anaphoric references and their
>> referents (e.g., inflexions, gender, different kinds of articles,
>> demonstratives, etc.). Some artificial languages (predicate
>> calculus, for example) replace all such mechanisms by variables,
>> which are, in effect, name-like labels.
>>
>> 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.
>
>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. (01)
Not necessarily. Think of ist as simply a
relation between contexts and propositions. The
proposition P is in fact either true or false:
suppose wlog it is true. However, the ist
relation may not hold between it and a certain
context C: this means that 'from the C point of
view' it would be considered 'false'. THis does
not mean it is in fact false, only that C takes a
different perspective on things. C's point of
view, at this juncture, is not veridical. But
this is entirely to do with the relation between
P and C, not with the actual truthvalue of P
(which itself bears no relation to C, and is
determined by the actual circumstances which
obtain, regardless of C; unless of course the
truth of the sentence expressing P depends in
some way on C.) (02)
> It could be thought that
>'proposition' here means the same as 'statement', but of course it is
>not the case, as you also say, explaining an earlier example, "the
>proposition is linked by statement relations (Stmt) to statements of the
>proposition", whereby statements and propositions are clearly distinguished.
>
>
>Furthermore, Pat Hayes wrote:
>
> > Propositions are not indexical or parameterized in any way. They are
>not sentences, which must be interpreted differently when the names
>which occur in them (actually, occur free in them) are reinterpreted. A
>proposition in IKL is an object which simply has a truth-value: it is a
>'bearer of truth'.
>
> > Yet another way to say it is to say that a proposition is like a
>sentence but with all its free names (and indexicals) already
>interpreted to refer to things. This has the consequence that
>propositional expressions are referentially transparent in IKL, so we
>had to invent an 'opaque name' construction to capture the intended
>meaning of opaque contexts.
>
>
>It surprises me, then to see in the IKL guide sentences such as
>
>(ist TemporalContextDay06-16-2006 (that (Dead Osama-Bin-Laden)))
>
>where apparently it is a proposition and not a sentence that is asserted
>to be true in a context. (Which in itself is not contradictory with the
>above, unless the hidden meaning is that the proposition is true in that
>context, put may be false in another. (03)
Yes indeed. And it may be true-in-a-context but
plain false, or vice versa. Its relationship to
contexts is completely independent of its
truth-value. To transcribe the relation ist as
meaning 'is true in' is purely an aid to
intuition: it has no bearing on the semantics of
the language. In IKL, "ist" is merely a relation
name, not a part of the logical syntax. (04)
> To be fully compatible with what
>Pat says above,
>
>(ist TemporalContextDay06-16-2006 (that (Dead Osama-Bin-Laden)))
>
>must mean exactly the same as
>
>(forall (c) (ist c (that (Dead Osama-Bin-Laden)))
>
>i.e., if a proposition is true in some context (so to speak, conflicting
>Pat's explanation above), it is true in any context whatsoever. (05)
Not at all. I hope the reason why not is clearer
now. Bear in mind that IKL assertions are 'simply
true', not 'true in a universal context' or 'true
in all contexts'. IKL is not a contextual logic:
it is simply a logic which we are using to talk
*about* things called contexts. (06)
>In the above example from IKL, it seems that the truth of the
>proposition *is* taken to be context-dependent, and that it includes an
>unresolved indexical -- a temporal one. (07)
No, it is not context-dependent. But the truth of
P, and the truth of (ist C P) , have nothing at
all to do with one another, and are determined
completely independently (as indeed they are in
most context logics). (08)
Pat (09)
>
>
>vQ
>
>
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