Pat Hayes wrote:
>> John F. Sowa schrieb:
>>> Wacek and Ingvar,
>>> It happens that English has no tenseless verb forms.
>>> In predicate calculus, you could write:
>>> ~(Ex)(rose(x) & blue(x)).
>>> This statement has no reference to any time or place.
>>> In English, it is possible to make a statement without
>>> reference to place, but not to time.
>> And isn't this the reason why Quine introduced his notion of 'eternal
>> sentence'? And propositions expressed by eternal sentences cannot change
>> truth-values, can they?
>>> vQ> The sentence "no roses are blue" was true some time ago,
>>> > and is false now; but does it correspond to the same
>>> > proposition in both cases?
>>> I would like to express the proposition stated by the
>>> above formula in predicate calculus. That statement
>>> is independent of any time, place, or context. The
>>> proposition it states has no unbound variables that
>>> could be bound, explicitly or implicitly, to any context.
>>> Yet that proposition can have different truth values
>>> in different contexts despite the fact that its meaning
>>> does not change.
>> Are you denying the old truth: 'same meaning, same reference'?
> Yes. The whole point of introducing 'contexts' is
> to provide for alternative views of what is true
> and what is not. The very same proposition may,
> in another context, have a different truthvalue.
> That is not to say it ACTUALLY has that
> truth-value: the ACTUAL truthvalue of any
> proposition is a given. But there is some utility
> in allowing the existence of entities which
> correspond to alternative ways the world might be
> (it allows one to reason about counterfactual or
> fictional circumstances, for example.) And when
> one does allow such things, it is pointless to
> insist that they must correspond to the way
> things actually are. So, we allow that a
> proposition may have a different truthvalue "in"
> a context than it has in fact. This does not
> actually make its truthvalue different from what
> it is, it simply introduces a new notion of
> truth-in-a-context. (01)
From this and the previous explanations, I think I get the point.
Thanks for the explanation, I did get the idea wrong. (02)
Would it not be better to say that a proposition p has a truth-value --
*the* truth-value of p -- which is not context-dependent in any way, but
that in different contexts it may be *said* to have another truth-value?
I think that "we allow that a proposition may have a different
truthvalue "in" a context than it has in fact" and "the very same
proposition may, in another context, have a different truthvalue" would
inevitably be misleading to most users, despite your clear (to me now)
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