Is Godel's system of axioms inconsistent?

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Discussion Overview

The discussion centers around the consistency of Gödel's system of axioms, specifically Zermelo-Fraenkel set theory with the Axiom of Choice (ZFC). Participants explore implications of Gödel's incompleteness theorems, the nature of consistency in mathematical systems, and the potential for statements to be provable or disprovable in different systems.

Discussion Character

  • Debate/contested, Technical explanation, Conceptual clarification

Main Points Raised

  • Some participants suggest that if Gödel's system is inconsistent, it could lead to the possibility of proving false statements as true.
  • Others argue that if a statement is unprovable in one consistent system, there exists another consistent system where the statement can be proven or disproven.
  • One participant notes that Gödel's theorem implies any consistent mathematical theory containing a model of the natural numbers is incomplete, highlighting the role of consistency in the theorem's proof.
  • Another participant questions whether the inability to prove ZFC's consistency is a direct consequence of Gödel's work, suggesting that consistency can be proven under certain conditions.

Areas of Agreement / Disagreement

Participants express differing views on the implications of Gödel's theorems regarding the consistency of ZFC, with no consensus reached on whether Gödel's results directly imply that ZFC cannot be proven consistent.

Contextual Notes

Some statements depend on specific interpretations of Gödel's theorems and the definitions of consistency and provability, which remain unresolved in the discussion.

Ursole
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As we cannot prove that Godel's system of axioms (ZFC?) is consistent, is it possible that it is inconsistent, that the Godel sentence is false, and that we yet prove it to be 'true'?
 
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When using an inconsistent system, any statement can be proven true.

If a statement is unprovable in one consistent system, then there is a consistent system in which this statement is provable, and there is another consistent system in which this statement is disprovable.
 
I.e., yes.

Godel's theorem says that "any consistent mathematical theory containing a model of the natural numbers is incomplete". (The conditions on the theory are a bit stronger than that, but the consistent requirement is part of the statement.)

If you follow his proof, you can see exactly where he assumes consistency of the theory, though it has been long enough that I have forgotten.
 
I may be wrong, but I don' t think it's a consequence of Godel that we can't prove ZFC consistent. We can prove all kinds of things to be consistent. What Godel says is that if we can write a formula in the language of ZFC that says "ZFC is consistent", then we can't prove it unless ZFC is really inconsistent.
 

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