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Article 6773 of comp.ai.philosophy:
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>From: weemba@sagi.wistar.upenn.edu (Matthew P Wiener)
Newsgroups: comp.ai.philosophy
Subject: Re: Marvin Minsky's Conscious Machines
Message-ID: <87847@netnews.upenn.edu>
Date: 3 Sep 92 17:40:19 GMT
References: <1992Aug13.025506.2404@news.media.mit.edu> <iordonez.714442640@academ01> <86891@netnews.upenn.edu> <iordonez.715293767@academ01>
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Reply-To: weemba@sagi.wistar.upenn.edu (Matthew P Wiener)
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In-reply-to: iordonez@academ01.mty.itesm.mx (Ivan Ordonez-Reinoso)

In article <iordonez.715293767@academ01>, iordonez@academ01 (Ivan Ordonez-Reinoso) writes:
>>>P: This sentence is not true.

>>>If senntence P were formalizable, it could be expressed in a logical
>>>finite formal system, which would require defining each of its elements.

>>Ways to formalize self-reference have been around for most of this
>>century.  Intuitively reasonable ones are new.  See, eg, Barwise and
>>Etchemendy(?) THE LIAR for two such.

>I don't know if this is supposed to prove that sentence P is formalizable,
>but anyway please note that in my original post I claimed that P is not
>formalizable because it contains a "not TRUE" part, and not because it
>is self referent. The concept "truth" is not formalizable.

Tarski's theorem is about the non-formalizability of a general truth
predicate.  It says nothing about particular instantiations of truth.
In particular, B&E show how to formalize "This sentence is true".

On a related note, Goedel's self-reference was indeed intuitively
reasonable, but it was limited in application.  So what I should have
said was that "intuitively reasonable, generally applicable" ones are
what is new.
-- 
-Matthew P Wiener (weemba@sagi.wistar.upenn.edu)


