Re: what makes it true?
- From: Robert Low <mtx014@xxxxxxxxxxxxxx>
- Date: Wed, 07 Sep 2005 14:55:58 +0100
Timothy Little wrote:
Torkel Franzen wrote:All models (of PA or some other theory, not of "the natural numbers") are of course equally real. What does this have to do with the observation - which is a simple mathematical theorem - that if GC is undecidable in PA (or in the much weaker theory Q), it is true?I may be mistaken, but isn't it a theorem that an undecidable proposition has both models where it is true and models where it is false? Why do you accept only the models in which it is true?
In this context, the word 'true' is understood (or is supposed to be understood) to mean 'true in the standard model'---you know, the set of objects that PA is supposed to be enabling you to reason about. The point is that PA fails to enable you to prove all the true statements about those objects. .
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