John F. Sowa schrieb:
> Folks,
> (01)
The discussion seems to have come to an end. Since I introduced the
question "what is a proposition?" into this forum, I would like to say
some concluding words on my part, too. That is, words from a philosopher
not interested in constructing formal-logical models or languages. But I
happen to be convinced that propositions are as needed in speech act
theoretical analyses of natural languages as they are in the
propositional calculus. (02)
> One reason for introducing a technical term, such as proposition,
> is to make distinctions that are confused in more common words
> such as 'meaning'. However, technical terms are always defined
> in some theory, and people who hold different theories are likely
> to have different and incompatible definitions.
> (03)
Sure; nonetheless: as far as I can see, everyone agrees (i) that
propositions are truthvalue bearers, and (ii) as soon as propositions
are tied to merely one world, one context, or one some-such-thing, then
the truthvalue of a proposition cannot possibly be changed. (I hope I am
allowed to use the word "changed" here, even though John wants to take
it away from IKL.)
> Quine has been cited as an authority, and he is for many purposes.
> But Q. has stated some strong views, which are not accepted by a
> large number of logicians and philosophers. (04)
Since I am the one who quoted Quine, let me make it clear that I quoted
him *only* in order to show that he is among the philosophers who regard
propositions (and/or their equvivalents such as 'eternal sentences') as
entities that cannot change truthvalues. I am by no means a Quinenan.
John Sowa has listed many respects in which his views differs from
Quine's. In all these respects, I share John's views; I even share his
critical stance towards much possible world talk. (05)
> In particular,
>
> 1. Q. rejected any version of modal logic. His opposition amounted
> to more than merely ignoring it while working on other issues.
> Instead, he denied the value, usefulness, or even the possibility
> of having a coherent system of modal logic.
>
> 2. Point #1 is compatible with Q's denial of any clear or coherent
> distinction between intension and extension. That distinction
> is central to any version of modal logic, which allows a sentence
> s (with no unresolved indexicals) to have different truth values
> in different worlds, contexts, or universes of discourse.
>
> 3. Since Q's primary work has been in formal logic, he never
> developed a complete semantics for natural languages (and he
> has been skeptical of the possibility of developing a complete
> semantics). Yet he made many comments about various sentences
> in NLs and their translations to logic.
>
> 4. In those comments, Q. avoided directly addressing the question
> of indexicals by coining the term 'eternal sentence' for a sentence
> whose referents are all fixed (either bound to explicit quantifiers
> or to explicitly named individuals). In effect, he defined that
> term to mean 'absence of indexicals' without using the terms
> 'indexical', 'context', 'possible world', etc.
>
> These views gave Quine's writings an admirable clarity, but at the
> expense of ignoring or even deprecating all talk about subjects he
> was not prepared to discuss clearly -- which includes the most serious
> issues about natural languages.
>
> For these reasons, I believe that taking the word 'proposition' as
> synonymous with Q's term 'eternal sentence' (06)
Surely, I have not proposed this; see my former remark! And I don't
think anyone else in this discussion has done it either. (07)
> would force us to adopt
> aspects of Q's philosophy that are incompatible with applications
> for which IKL (and other logics) might be used. Among them is the
> semantics of NLs, for which many people would like to use IKL.
>
> Since IKL uses the word 'proposition' as a technical term, it is
> important to use that word in a way that minimizes confusion among
> IKL adopters. (08)
But when it is introduced in a forum like "ontolog-forum", I think it is
equally important to introduce it in such a way that even confusion
among the members of the forum that are not IKL adopters is minimized. (09)
> I think I agree with Pat about the IKL formalism,
> and I think that I know what he meant by the following statements:
>
> 1. A proposition has a fixed truth value.
>
> 2. But a proposition might have different truth values in different
> contexts.
>
> However, this conjunction is likely to cause confusion (or at least
> lengthy discussions such as this thread).
>
> My recommendation is to replace the above statements with something
> along the following lines:
>
> 1. The IKL model theory defines an evaluation function Phi, which
> for any proposition p, determines a truth value Phi(p).
>
> 2. Inside a nested context, however, the proposition p could have
> a truth value that is different from the value Phi(p) that would
> be determined outside any nested context.
>
> This avoids the word 'fixed' without introducing the word 'changing'
> or any term such as 'proposition-in-a-context'.
> (010)
At last, may I humbly repeat an earlier (but unanswered) mail-question
of mine; even if perhaps it is based on a complete misunderstanding of
IKL. Here the mail once again: (011)
------------------------------------------------------------------ (012)
Waclaw Kusnierczyk schrieb: (013)
> > I think we agree. A context, as treated in IKL, corresponds to a
> > perspective (no cognitive agent implied) on a proposition *as if it
> > were* true or false, irrespectively of whether it *is* true or false.
> >
> (014)
Dear Waclaw, (015)
Does this solve the following earlier problem of yours: "The question,
again, is about propositions. 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? Is it the proposition that changed its truth
value, or are we really dealing with two distinct propositions: 'no
roses are blue at t1', and 'no roses are blue at t2'?" ? (016)
If "no roses are blue" are stated twice (in the way you have described)
*in the same context*, then it seems to me that a distinction such as
mine between *sentence meaning* and *used sentence meanings* is
nonetheless needed as a complement. (017)
----------------------------------------------- (018)
Is my question completely beside the point? Is IKL not at all meant to be
applied to the kind of
natural language situations that I am envisaging? If so, then there is of
course no need to discuss how to individuate propositions in natural languages.
Can someone, please, tell me whether IKL has or is meant to be given some kind
of relation to natural languages. (019)
best wishes,
Ingvar (020)
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