From: Harvey Newstrom (mail@HarveyNewstrom.com)
Date: Sat May 25 2002 - 12:02:09 MDT
On Saturday, May 25, 2002, at 11:45 am, Lee Corbin wrote:
> Quite right. One has to be very careful with logic. Consider
> the following theorem:
>
> Theorem: God Exists.
>
> Proof: If this sentence is true, then God exists. Therefore,
> God exists because that sentence is indeed true. How do we
> know that it's true? Simple. A sentence is true when the claim
> that it makes is correct (or true). Well, what claim does that
> sentence make? It claims that if it itself were true, then God
> would exist. But that's so! If indeed the sentence were true,
> then God would exist. Since what the sentence claims is so, then
> the sentence is true, and so God exists. Q.E.D.
>
> There is *no* logical flaw in the above proof, despite the
> frenzied attempts it will provoke to find a flaw. The flaw
> in the proof is semantical, not logical. It turns out that
> words cannot always be thrown around with impunity---careful
> thought and good judgment are always necessary.
I disagree. This is an extremely clear example of the classical logical
fallacy known as "circular logic." The first sentence refers to
itself. The resolution is provides is a restatement of its conditional
proposition. The "if" statement cannot be resolved without recursively
invoking another "if". No determination is possible without the same
question being raised again at the next iteration.
Unlike less clear examples, this sentence actually contains the subject
of "this sentence" in referencing itself. I can't imagine a more
explicit example of a circular logic violation than this. I can't
imagine how assert that there is no logical flaw in the above proof,
when the flaw is so explicit, classic and basic. This would be covered
in the first day of any freshman logic course.
-- Harvey Newstrom, CISSP <www.HarveyNewstrom.com> Principal Security Consultant <www.Newstaff.com>
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