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|    sci.logic    |    Logic -- math, philosophy & computationa    |    262,912 messages    |
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|    Message 262,697 of 262,912    |
|    Mikko to olcott    |
|    Re: The Halting Problem asks for too muc    |
|    24 Jan 26 10:20:59    |
      XPost: sci.math, comp.theory       From: mikko.levanto@iki.fi              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.              --       Mikko              --- SoupGate-Win32 v1.05        * Origin: you cannot sedate... all the things you hate (1:229/2)    |
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