That for a certain broad class of systems with certain qualities the consistency of same cannot be proved within the system is demonstrated as a consequence of Godel's theorem's. But you do not appear to be acknowledging that the proofs in question are meta-mathematical. — tim wood
Well any demonstration of axiomatic
incompleteness is a purely
syntactical demonstration, in spite of any semantic or meta-logical pretenses to the contrary. It purely consists in the exhibition of a well-formed formula f and it's negation ~f , in a circumstance where neither is currently known to be syntactically inconsistent in relation to a given set of axioms.
The fact that it is possible to prove the
relative consistency of PA in relation to the
relative consistency of another system, is again, an equally syntactical derivation, whilst the syntactical notion of
absolute inconsistency is also potentially observable by deriving f & ~f. But i don't understand the notion called
absolute consistency. For that seems akin to the idea of 'completed infinity'; both of these notions are
impossible to determine, or even to define in a non-circular fashion, and only serve to disguise the under-determined semantics of logic that is actually decided
a posteriori when a sentence is actually derived, proved, or else used in a fashion unrelated to logic.
No it isn't. I'm thinking you've read the proof and worked through it at least some - but maybe not. The universal quantifiers are then qualified via recursion schema. . — tim wood
I was referring to the
cause of incompleteness, which is due to unbounded universal quantification in cases where universal quantifiers cannot be eliminated. Although here I made a mistake, in that the origin of incompleteness in weaker systems than Peano Arithmetic lies with the universal quantifiers in the
other arithmetic axioms, as opposed to the axiom of induction - as evidenced by the incompleteness of Robinson arithmetic that does not possess the induction axiom. None of this changes anything of significance tho..
And significantly, while your Prov("X," "S") is recursive, according to Godel, Godel also says the related Provable ("S"); that is, "S is a provable theorem," is not recursive. — tim wood
And hence the reason why the universal quantifier over ~Prov('S','G') to form ~prov('G') should not be interpreted as literally "passing over"
every number, which was my original point. For Prov('G') might still be derivable, even though Prov('S','G') isn't actually derivable for any 'S', if PA turns out to be omega inconsistent. Likewise, ~Prov('G')
cannot express the fact that Prov('S','G')
is not derivable for some 'S', for then the diagonalisation lemma yields the contradiction t => ~Prov(''t') for some t.
The sentence t => ~Prov("t") has an infinitely expandable fractal-like structure due to the sentence being fed it's own godel number, and there is no known reduction of it's quantifiers to those of the axioms. Therefore, whether or not PA is consistent, we don't have a semantically interpretable sentence. All we have is a syntactically verifiable self-negating sentence that has no meaningful interpretation.
The ultimate mistake is this: In logic, the absence of a witness should not be equivocated with the witnessing of an absence. Only by making this conflation, as is done in classical logic, can Godel's sentence assume its controversial and illogical interpretation as proving it's non-provability.
It is disingenuous sophistry of textbooks to suggest that t => ~Prov("t") has the high-level interpretation "t implies that t doesn't have a proof", even with the consistency disclaimers. Worse, it disguises the synthetic a posteriori nature of reasoning.
An existential quantifier cannot make a non-trivial existential
claim. Either the quantifier concerned is analytically reducible to an instance of the axioms, else the quantifier is logically meaningless and should not even be informally interpreted.
So it appears to me, so far, that you're the guy that says "prove it" to the respective proofs until they're driven into their own grounding in axioms and sense, at which level the call for proof is an error. Are you that guy?
That is, I do not take you to be challenging or disqualifying Godel, but rather making some assumptions both counter-to and beyond it, for other purposes. As you say above, — tim wood
On the contrary, I'm about eliminating unprovable assumptions from popular understandings of logic.