Re: Goedel applied to the real-world

From: Barb Knox (see_at_sig.below)
Date: 11/17/04

  • Next message: George Greene: "Re: Cantor's diagonal proof wrong?" 
    Date: Wed, 17 Nov 2004 13:36:35 +1300

    In article <3df1e59f.0411161611.2e342cb6@posting.google.com>,
     chvol@aol.com (Charlie-Boo) wrote:

    >Barb Knox <see@sig.below> wrote
    >> In article <3df1e59f.0411150038.7eea13da@posting.google.com>,
    >> chvol@aol.com (Charlie-Boo) wrote
    >
    >> >How about:
    >> >
    >> >1. "This is not true." has no truth value.
    >>
    >> Unfortunately this approach fails, since by Tarski's theorem "xxx is true"
    >> is not consistently expressible by any predicate at all in whatever formal
    >> language one is using here.
    >
    >We can't say that "This is not true" has no truth value?

    More basically, we can't even EXPRESS (in an appropriate formal language)
    "This is not true". If we can't even express it in the first place then we
    surely can't say anything about it.

    >Then it DOES have a truth value?

    Eh? "It" can not be formally expressed in the first place, so you can't say
    ANYTHING formally about it (including anything about its hypothetical truth
    value).

    >Ok, what is the truth value of "This is not true."?

    That's only a meaningful question if the predicate True can be defined in
    the first place, which by Tarski's theorem it can not be.

    [snip] 

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