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|    Message 262,724 of 262,912    |
|    olcott to Mikko    |
|    Re: The Halting Problem asks for too muc    |
|    25 Jan 26 07:24:09    |
      XPost: sci.math, comp.theory       From: polcott333@gmail.com              On 1/25/2026 5:19 AM, Mikko wrote:       > On 24/01/2026 16:01, olcott wrote:       >> On 1/24/2026 2:20 AM, Mikko wrote:       >>> On 23/01/2026 12:22, olcott wrote:       >>>> On 1/23/2026 3:13 AM, Mikko wrote:       >>>>> On 22/01/2026 18:40, olcott wrote:       >>>>>> On 1/22/2026 2:21 AM, Mikko wrote:       >>>>>>> On 21/01/2026 17:22, olcott wrote:       >>>>>>>> On 1/21/2026 3:03 AM, Mikko wrote:       >>>>>>>>>       >>>>>>>>> No, it hasn't. In the way theories are usually discussed       >>>>>>>>> nothing is       >>>>>>>>> "ture in arithmetic". Every sentence of a first order theory that       >>>>>>>>> can be proven in the theory is true in every model theory. Every       >>>>>>>>> sentence of a theory that cannot be proven in the theory is false       >>>>>>>>> in some model of the theory.       >>>>>>>>>       >>>>>>>>>> only because back then proof theoretic semantics did       >>>>>>>>>> not exist.       >>>>>>>>>       >>>>>>>>> Every interpretation of the theory is a definition of semantics.       >>>>>>>>>       >>>>>>>>       >>>>>>>> Meta‑math relations about numbers don’t exist in PA       >>>>>>>> because PA only contains arithmetical relations—addition,       >>>>>>>> multiplication, ordering, primitive‑recursive predicates       >>>>>>>> about numbers themselves—while relations that talk about       >>>>>>>> PA’s own proofs, syntax, or truth conditions live entirely       >>>>>>>> in the meta‑theory;       >>>>>>>       >>>>>>> Methamathematics does not need any other relations between numbers       >>>>>>> than what PA has. But relations that map other things to numbers       >>>>>>> can be useful for methamathematical purposes.       >>>>>>>       >>>>>>>> so when someone appeals to a Gödel‑style relation like       >>>>>>>> “n encodes a proof of this very sentence,” they’re       >>>>>>>> invoking a meta‑mathematical predicate that PA cannot       >>>>>>>> internalize, which is exactly why your framework draws       >>>>>>>> a clean boundary between internal proof‑theoretic truth       >>>>>>>> and external model‑theoretic truth.       >>>>>>>       >>>>>>> Anyway, what can be provven that way is true aboout PA. You can deny       >>>>>>> the proof but you cannot perform what is meta-provably impossible.       >>>>>>       >>>>>> Gödel’s sentence is not “true in arithmetic.”       >>>>>> It is true only in the meta‑theory, under an       >>>>>> external interpretation of PA (typically the       >>>>>> standard model ℕ). Inside PA itself, the sentence       >>>>>> is not a truth‑bearer at all.       >>>>>       >>>>> There is no concept of "truth-bearer" in an uninterpreted theory       >>>>> because       >>>>> there is not concept of "truth". The relevant concept is "sell-formed-       >>>>> formula" and Gödels sentence is one. It may be true or false in an       >>>>> interpretation.       >>>       >>>> There is a       >>>> "true on the basis of meaning expressed in language"       >>>> and I figured out how to make it computable over the       >>>> body of knowledge.       >>>       >>> Except that "true on the basis of meaning expressed in language" is       >>> nmt computable and does not cover all of the body of knowldge.       >>       >> When the basis of "true" is proof theoretic semantics       >> internal to the formal system relative to its own axioms       >> and not truth conditional in a separate model outside       >> of the system undecidability ceases to exist.       >       > No, it does not. It does not matter what you call it, a sentence       > that cannot be neither proven nor disproven is undecidable because       > that is what the word means. An example is Gödel's sentence in       > Peano arithmetics.       >              When a truth predicate gets the input "What time is?"       this input is rejected as not truth-apt.              When PA gets an expression that cannot be proven or       refuted using its own axioms then this expression is       not within its domain.                     --       Copyright 2026 Olcott |
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