Skepdick wrote: ↑Fri Apr 21, 2023 9:08 pm
PeteOlcott wrote: ↑Fri Apr 21, 2023 9:08 pm
None-the-less the proof of G in F does require a sequence of inference steps in F that proves that no such sequence exists in F.
"The proof of G in F" is a meaningless statement.
Which property of G (in F) are you proving?
When G asserts that it is unprovable in F it is asserting
that there is no sequence of inference steps in F that derives G.
The reason why G is unprovable in F is that a proof of G in F:
(1) Requires a sequence of inference steps (as all proof do) in F.
(2) These same inference steps in F must prove that they themselves do not exist in F.
A thing cannot prove that itself doesn't exist.
So Gödel proves G in Meta-F where G is not contradictory.
Tarski made the same mistake:
This sentence is not true: "This sentence is not true"
The inner sentence is in his theory and the outer sentence is in his meta-theory.
He concluded that because he could not prove that the inner sentence is true
in his theory yet could prove that the outer sentence is true in his meta-theory
That some true statements cannot be defined in a single theory and must rely
on an infinite hierarchy of meta-theories.
He never noticed that the inner sentence is simply not a truth bearer.