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

To: "[ontolog-forum]" <ontolog-forum@xxxxxxxxxxxxxxxx>
From: Waclaw Kusnierczyk <Waclaw.Marcin.Kusnierczyk@xxxxxxxxxxx>
Date: Wed, 30 May 2007 08:47:07 +0200
Message-id: <465D1DEB.7080804@xxxxxxxxxxx>

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) 
intentions.    (03)

vQ    (04)

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