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Re: Why is model theory needed?

Newsgroups sci.logic
Date 2023-04-09 10:15 -0700
References <u0sejc$1cb2d$1@dont-email.me> <8cd83c97-2e16-4fa9-8d6a-cd95195ffa04n@googlegroups.com> <7c6b1210-51e4-4b99-874c-a4d80d6fae6cn@googlegroups.com> <07bb8271-be61-4da3-b26e-048255ab059bn@googlegroups.com>
Message-ID <0a37e2de-e793-44e2-872e-d9581812bf29n@googlegroups.com> (permalink)
Subject Re: Why is model theory needed?
From Mostowski Collapse <bursejan@gmail.com>

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But when did modern model theory start? What one would
nowadays hear in an university course about model theory?
It surely not Skolem paradox and non-categoricity of set theory.

In first-order logic, only theories with a finite model can 
be categorical. So what is usually meant by categoricity in
FOL is something weaker, and it can be defined without

model theory, namely. A theory T is  complete:

For every formula A either T |- A or T |- ~A.

And incomplete theory is automatically non-categorical.
How would you show that an incomplete theory is
non-categorical, with what peopel would learn today

in an university course about model theory?

Mitchell Smith schrieb am Sonntag, 9. April 2023 um 17:22:47 UTC+2:
> On Sunday, April 9, 2023 at 9:56:50 AM UTC-5, Mostowski Collapse wrote: 
> 
> The best answer, Jan, is probably with de Morgan and Peacock. I have not read Peacock, but, I can provide quotes from de Morgan's work on double algebra. Among other things, he explicitly discusses how an untrained intellect discovering a formal algebra is likely to apply an interpretation of the symbols independent from the intended interpretations of the original authors. 
> 
> One can probably relate this to the inscrutability of reference argument attributed to Quine. 
> 
> De Morgan's problem had been that signs for operations appeared to have the same functions across different types of numbers. Prior to complex numbers and quaternions, no one had actually noticed the problem. Thus, the meaning of operation symbols became relegated to the specification of a domain of discourse. 
> 
> The algebraic picture is re-introduced into "foundations" when Skolem points out that Zermelo's set theory cannot be categorical. Skolem also recognizes that the same is true of arighmetic and is credited with the first recognitikn of non-standard models. 
> 
> Gotta go.... can say more later. 
> 
> mitch
> > Quizz: And when did Model Theory start? In its modern form? 
> > I mean mentioning Kant and Newton is Ok, but does it help to 
> > give a picture of **modern** Model Theory. When did it start? 
> > Mitchell Smith schrieb am Sonntag, 9. April 2023 um 16:01:54 UTC+2: 
> > > On Saturday, April 8, 2023 at 2:17:04 PM UTC-5, olcott wrote: 
> > > > Well-formed formulas have meaning only when an interpretation is given 
> > > > for the symbols. Mendelson 
> > > > 
> > > > No one seems to know why model theory is needed. 
> > > > A ∧ B → A is known to be true on the basis of the meaning of the 
> > > > symbols, no model theory needed. 
> > > > 
> > > > -- 
> > > > Copyright 2023 Olcott "Talent hits a target no one else can hit; Genius 
> > > > hits a target no one else can see." Arthur Schopenhauer 
> > > Peter, 
> > > 
> > > A similar question had been asked on MSE two years ago. I have no reason to join the auspicious minds of MSE (who practice censorship), but, I have occasionally answered as a guest. 
> > > 
> > > I gave a two-part answer to the question at the link, 
> > > 
> > > https://math.stackexchange.com/questions/3970711/what-is-the-point-of-model-theory 
> > > 
> > > under 'mls'. 
> > > 
> > > You may find it informative. The original poster did accept my answer.

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Why is model theory needed? olcott <polcott2@gmail.com> - 2023-04-08 14:16 -0500
  Re: Why is model theory needed? Ross Finlayson <ross.a.finlayson@gmail.com> - 2023-04-08 12:36 -0700
    Re: Why is model theory needed? olcott <polcott2@gmail.com> - 2023-04-08 14:40 -0500
      Re: Why is model theory needed? Ross Finlayson <ross.a.finlayson@gmail.com> - 2023-04-08 12:51 -0700
  Re: Why is model theory needed? André G. Isaak <agisaak@gm.invalid> - 2023-04-08 14:27 -0600
    Re: Why is model theory needed? olcott <polcott2@gmail.com> - 2023-04-08 15:35 -0500
    Re: Why is model theory needed? [superb answer] olcott <polcott2@gmail.com> - 2023-04-08 16:04 -0500
      Re: Why is model theory needed? [superb answer] André G. Isaak <agisaak@gm.invalid> - 2023-04-08 15:15 -0600
        Re: Why is model theory needed? [superb answer] olcott <polcott2@gmail.com> - 2023-04-08 16:23 -0500
          Re: Why is model theory needed? [superb answer] André G. Isaak <agisaak@gm.invalid> - 2023-04-08 15:34 -0600
            Re: Why is model theory needed? [superb answer] Julio Di Egidio <julio@diegidio.name> - 2023-04-08 14:43 -0700
            Re: Why is model theory needed? [superb answer] olcott <polcott2@gmail.com> - 2023-04-08 17:51 -0500
              Re: Why is model theory needed? [superb answer] André G. Isaak <agisaak@gm.invalid> - 2023-04-08 17:05 -0600
                Re: Why is model theory needed? [superb answer] olcott <polcott2@gmail.com> - 2023-04-08 18:20 -0500
                Re: Why is model theory needed? [superb answer] André G. Isaak <agisaak@gm.invalid> - 2023-04-08 17:30 -0600
                Re: Why is model theory needed? [superb answer] Ross Finlayson <ross.a.finlayson@gmail.com> - 2023-04-08 16:35 -0700
                Re: Why is model theory needed? [superb answer] Julio Di Egidio <julio@diegidio.name> - 2023-04-08 16:45 -0700
                Re: Why is model theory needed? [superb answer] Ross Finlayson <ross.a.finlayson@gmail.com> - 2023-04-08 17:12 -0700
                Re: Why is model theory needed? [superb answer] Julio Di Egidio <julio@diegidio.name> - 2023-04-08 17:17 -0700
                Re: Why is model theory needed? [superb answer] olcott <polcott2@gmail.com> - 2023-04-08 19:25 -0500
                Re: Why is model theory needed? [superb answer] olcott <polcott2@gmail.com> - 2023-04-08 19:21 -0500
                Re: Why is model theory needed? [superb answer] André G. Isaak <agisaak@gm.invalid> - 2023-04-08 18:46 -0600
                Re: Why is model theory needed? [superb answer] Julio Di Egidio <julio@diegidio.name> - 2023-04-08 17:52 -0700
                Re: Why is model theory needed? [superb answer] André G. Isaak <agisaak@gm.invalid> - 2023-04-08 18:57 -0600
                Re: Why is model theory needed? [superb answer] Julio Di Egidio <julio@diegidio.name> - 2023-04-08 18:00 -0700
                Re: Why is model theory needed? [superb answer] Julio Di Egidio <julio@diegidio.name> - 2023-04-08 18:27 -0700
                Re: Why is model theory needed? [superb answer] olcott <polcott2@gmail.com> - 2023-04-08 20:30 -0500
                Re: Why is model theory needed? [superb answer] Ross Finlayson <ross.a.finlayson@gmail.com> - 2023-04-08 19:12 -0700
                Re: Why is model theory needed? [superb answer] Julio Di Egidio <julio@diegidio.name> - 2023-04-09 02:41 -0700
                Re: Why is model theory needed? [superb answer] olcott <polcott2@gmail.com> - 2023-04-08 20:21 -0500
                Re: Why is model theory needed? [superb answer] Julio Di Egidio <julio@diegidio.name> - 2023-04-08 16:23 -0700
                Re: Why is model theory needed? [superb answer] Julio Di Egidio <julio@diegidio.name> - 2023-04-08 16:25 -0700
    Re: Why is model theory needed? [superb answer][model] olcott <polcott2@gmail.com> - 2023-04-11 08:54 -0500
  Re: Why is model theory needed? Mostowski Collapse <bursejan@gmail.com> - 2023-04-09 03:30 -0700
  Re: Why is model theory needed? Mitchell Smith <mitchellsmith0860@gmail.com> - 2023-04-09 07:01 -0700
    Re: Why is model theory needed? Mostowski Collapse <bursejan@gmail.com> - 2023-04-09 07:56 -0700
      Re: Why is model theory needed? Mitchell Smith <mitchellsmith0860@gmail.com> - 2023-04-09 08:22 -0700
        Re: Why is model theory needed? Mostowski Collapse <bursejan@gmail.com> - 2023-04-09 10:15 -0700
          Re: Why is model theory needed? Mitchell Smith <mitchellsmith0860@gmail.com> - 2023-04-09 19:16 -0700
            Re: Why is model theory needed? Mostowski Collapse <bursejan@gmail.com> - 2023-04-09 23:40 -0700
              Re: Why is model theory needed? Mostowski Collapse <bursejan@gmail.com> - 2023-04-10 00:02 -0700
                Re: Why is model theory needed? Mostowski Collapse <bursejan@gmail.com> - 2023-04-10 01:05 -0700
                Re: Why is model theory needed? Mitchell Smith <mitchellsmith0860@gmail.com> - 2023-04-10 04:59 -0700
                Re: Why is model theory needed? Mostowski Collapse <bursejan@gmail.com> - 2023-04-10 08:59 -0700
                Re: Why is model theory needed? Mostowski Collapse <bursejan@gmail.com> - 2023-04-10 09:11 -0700
                Re: Why is model theory needed? [true] olcott <polcott2@gmail.com> - 2023-04-10 11:50 -0500
                Re: Why is model theory needed? [true] Mostowski Collapse <bursejan@gmail.com> - 2023-04-11 00:20 -0700
                Re: Why is model theory needed? [true] olcott <polcott2@gmail.com> - 2023-04-11 08:00 -0500
                Re: Why is model theory needed? [true] Mostowski Collapse <bursejan@gmail.com> - 2023-04-11 10:21 -0700
                Re: Why is model theory needed? [true] olcott <polcott2@gmail.com> - 2023-04-11 12:36 -0500
                Re: Why is model theory needed? [true] olcott <polcott2@gmail.com> - 2023-04-11 12:39 -0500
                Re: Why is model theory needed? [true] Mostowski Collapse <bursejan@gmail.com> - 2023-04-11 11:26 -0700
                Re: Why is model theory needed? [true] olcott <polcott2@gmail.com> - 2023-04-11 13:34 -0500
                Re: Why is model theory needed? [true] Mostowski Collapse <bursejan@gmail.com> - 2023-04-11 11:37 -0700
                Re: Why is model theory needed? [true] Julio Di Egidio <julio@diegidio.name> - 2023-04-11 21:19 -0700
                Re: Why is model theory needed? [true] Julio Di Egidio <julio@diegidio.name> - 2023-04-11 22:49 -0700
                Re: Why is model theory needed? [true] Julio Di Egidio <julio@diegidio.name> - 2023-04-12 08:36 +0200
                Re: Why is model theory needed? [true] Julio Di Egidio <julio@diegidio.name> - 2023-04-11 23:47 -0700
                Re: Why is model theory needed? [true] Julio Di Egidio <julio@diegidio.name> - 2023-04-12 00:29 -0700
                Re: Why is model theory needed? [true] Julio Di Egidio <julio@diegidio.name> - 2023-04-12 16:15 +0200
                Re: Why is model theory needed? [true] Mostowski Collapse <bursejan@gmail.com> - 2023-04-12 07:49 -0700
                Re: Why is model theory needed? [true] Mostowski Collapse <bursejan@gmail.com> - 2023-04-12 07:51 -0700
                Re: Why is model theory needed? [true] [Montague Grammar] olcott <polcott2@gmail.com> - 2023-04-12 10:22 -0500
                Re: Why is model theory needed? [true] [Montague Grammar] Mostowski Collapse <bursejan@gmail.com> - 2023-04-12 10:02 -0700
                Re: Why is model theory needed? [true] [Montague Grammar] Mostowski Collapse <bursejan@gmail.com> - 2023-04-12 10:10 -0700
                Re: Why is model theory needed? [true] [Montague Grammar] olcott <polcott2@gmail.com> - 2023-04-12 13:21 -0500
                Re: Why is model theory needed? [true] [Montague Grammar] Ross Finlayson <ross.a.finlayson@gmail.com> - 2023-04-12 11:56 -0700
                Re: Why is model theory needed? [true] [Montague Grammar] Julio Di Egidio <julio@diegidio.name> - 2023-04-12 11:59 -0700
                Re: Why is model theory needed? [true] [Montague Grammar] Ross Finlayson <ross.a.finlayson@gmail.com> - 2023-04-12 12:13 -0700
                Re: Why is model theory needed? [true] Julio Di Egidio <julio@diegidio.name> - 2023-04-12 19:48 +0200
                Re: Why is model theory needed? [true] Mostowski Collapse <bursejan@gmail.com> - 2023-04-12 11:11 -0700
                Re: Why is model theory needed? [true] Julio Di Egidio <julio@diegidio.name> - 2023-04-12 11:53 -0700
                Re: Why is model theory needed? [true] olcott <polcott2@gmail.com> - 2023-04-12 14:12 -0500
                Re: Why is model theory needed? [true] Julio Di Egidio <julio@diegidio.name> - 2023-04-12 12:17 -0700
                Re: Why is model theory needed? [true] Mostowski Collapse <bursejan@gmail.com> - 2023-04-17 07:53 -0700
                Re: Why is model theory needed? [true] Ross Finlayson <ross.a.finlayson@gmail.com> - 2023-04-11 22:35 -0700
                Re: Why is model theory needed? [true] Ross Finlayson <ross.a.finlayson@gmail.com> - 2023-04-12 12:28 -0700
                Re: Why is model theory needed? [true] Julio Di Egidio <julio@diegidio.name> - 2023-04-12 12:33 -0700
                Re: Why is model theory needed? [true] Ross Finlayson <ross.a.finlayson@gmail.com> - 2023-04-12 13:29 -0700
                Re: Why is model theory needed? [true] Mostowski Collapse <bursejan@gmail.com> - 2023-04-12 14:04 -0700
                Re: Why is model theory needed? [true] Mostowski Collapse <bursejan@gmail.com> - 2023-04-12 14:06 -0700
                Re: Why is model theory needed? [true] Ross Finlayson <ross.a.finlayson@gmail.com> - 2023-04-12 14:14 -0700
                Re: Why is model theory needed? [true] Ross Finlayson <ross.a.finlayson@gmail.com> - 2023-04-12 14:16 -0700
              Re: Why is model theory needed? Mitchell Smith <mitchellsmith0860@gmail.com> - 2023-04-10 04:16 -0700
    Re: Why is model theory needed? olcott <polcott2@gmail.com> - 2023-04-09 10:01 -0500
      Re: Why is model theory needed? Mostowski Collapse <bursejan@gmail.com> - 2023-04-09 08:15 -0700
        Re: Why is model theory needed? olcott <polcott2@gmail.com> - 2023-04-09 10:18 -0500
      Re: Why is model theory needed? Mitchell Smith <mitchellsmith0860@gmail.com> - 2023-04-09 17:51 -0700
        Re: Why is model theory needed? [truth v provability] olcott <polcott2@gmail.com> - 2023-04-10 13:12 -0500
          Re: Why is model theory needed? [truth v provability] Mitchell Smith <mitchellsmith0860@gmail.com> - 2023-04-12 19:15 -0700
            Re: Why is model theory needed? [truth v provability] Julio Di Egidio <julio@diegidio.name> - 2023-04-12 19:34 -0700
            Re: Why is model theory needed? [truth v provability] olcott <polcott2@gmail.com> - 2023-04-12 22:40 -0500
              Re: Why is model theory needed? [truth v provability] Mitchell Smith <mitchellsmith0860@gmail.com> - 2023-04-13 19:44 -0700
                Re: Why is model theory needed? [truth v provability] olcott <polcott2@gmail.com> - 2023-04-13 22:29 -0500
                Re: Why is model theory needed? [truth v provability] Ross Finlayson <ross.a.finlayson@gmail.com> - 2023-04-14 11:17 -0700
                Re: Why is model theory needed? [truth v provability] olcott <polcott2@gmail.com> - 2023-04-15 13:43 -0500
            Re: Why is model theory needed? [truth v provability] olcott <polcott2@gmail.com> - 2023-04-15 23:22 -0500

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