Re: On the definition of "ontology" (Paul van der Vet)
Date: Fri, 6 Oct 1995 10:49:14 +0100
From: (Paul van der Vet)
Message-id: <>
Subject: Re: On the definition of "ontology"
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At 10/4/95, Pat Hayes wrote:

> At  2:30 PM 10/4/95 +0100, Paul van der Vet wrote:
> > [...] when you develop a
> >knowledge-based system you'll have one intended model in mind.
> This raises an interesting issue (which may be getting too philosphical for
> skrb, but here goes anyway.)

I didn't mean to raise *that* issue, of course. But it's near weekend,
I've finished the stuff I should have finished two weeks ago, so let's
indulge ...

> What one 'has in mind' is presumably expressed
> there in some mental representation. Now, how do we know that this
> mentalese representation in fact has unique models? All the lessons of
> logic would suggest that it usually doesn't; that usually there will be
> nonstandard models of our thoughts. (This will almost certainly be true,
> for example, if theoremhood in our mentalese is RE and it is given a
> semantics which reflects this accurately.) 
> Now, if this is the case, then what warrant can we have for insisting that
> there is "a" model that we have in mind? We have no special access to
> models of our mental language: we can only think of things IN that
> language. 

Let's, for the sake of argument, take the leap of faith for granted and
assume we have some device to read our mind.

- Would we obtain a theory in logic or a theory plus model? If the
latter, it is again a logical theory since it is a bundle of thoughts
(at least, so I understand Pat). Tarski could pull the trick of having
the recursion `bottom out' at the level of natural language (the
"absolute" meta-level). We are prevented from doing the same because
language originates in thought and there we go again. In other words,
the idea of model-theoretic semantics for thoughts (*if* they are
present? expressed? in a logical theory) may be incoherent.

- There are semantics other than model-theoretic such as update
semantics and Kowalski's closely related `logic without models' idea.
The incoherence objection doesn't apply, but in adopting these
semantics we loose some of the advantages of model-theoretic


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