Logic and Language

Logic and Language

Copyright © James R Meyer 2012 - 2018 www.jamesrmeyer.com

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In an article entitled ‘Yablo Without Gödel’ (Footnote: Volker Halbach, and Shuoying Zhang, *Yablo without Gödel* (PDF). Analysis, 77(1), 53-59, 2016) in the journal Analysis, (Footnote: Analysis is published quarterly by the Oxford University Press on behalf of the Analysis Trust, see also the Wikipedia entry) Halbach & Zhang claim that they can generate the Yablo paradox (Footnote: Stephen Yablo. *Paradox Without Self-Reference*, Analysis 53 (4): pages 251-252. 1993. It can be viewed Paradox Without Self-Reference: here.) without using any circularity or self-reference, and without using methods such as the diagonal lemma or Gödel numbering.

However, they make a ridiculous assumption that renders their claim of a proof utterly laughable. It is also rather amusing that the journal Analysis proudly proclaims on their website that it is the “*most established and esteemed journal for short papers in philosophy. We are happy to publish excellent short papers …*.” Apparently they are also very happy to publish complete crap.

In defining a formal language, Halbach & Zhang state:

We work in a language [ T ] of predicate logic. Apart from the identity symbol, the language contains a binary predicate symbol <, and a ternary predicate symbol *Sat*(*x*, *y*, *z*). For each formula **φ** in the language, there is a closed term **φ** in the language. This can be achieved by adding countably many new constants, *c*_{1}, *c*_{2}, … to the language and then fixing some 1-1-mapping between the set of constants and the set of formulae in the language with all constants. This mapping doesn’t play any role in the proof of the paradox; it only helps to motivate our version TS of the T-sentences below. No assumptions about the structure of sentences are used in our proof. We write **φ** for the constant for **φ**.

Halbach and Zhang specifically refer to one single language which includes all the terms that they refer to, including the postulated enumeration function **φ** (where **φ** is the free variable of the function **φ** ) within that same language. But although Halbach and Zhang assert that all these terms belong to the same language, they do not provide any proof that it is possible that the function **φ** can be in that same language. In fact, as shown below, it is trivially easy to show that it is impossible.

Halbach & Zhang assert that whenever the free variable **φ** in the function **φ** is substituted by a valid substitution value, the result is a closed term, that is, the term can have no free variables. But if the substitution value is a formula with one or more free variables, then, since all terms belong to the * same language*, (Footnote: In Halbach & Zhang’s account, only one language is involved and there is no mention of a meta-language.) the resultant term is necessarily a term that contains one or more free variables that are not subject to a quantifier, and yet Halbach & Zhang assert that the term is closed and has no free variables. For example, if the substituted value is

It is worth pointing out here that, besides the obvious claim implicit in the title of their article, Halbach & Zhang specifically assert that their claim relies neither on Gödel numbering nor the diagonal lemma, and moreover, make no mention of a meta-language (Gödel numbering is a function in a meta-language to the language being coded).

Halbach & Zhang discover that their system results in a contradiction. That’s not a surprise to me. But the astonishing thing is that Halbach & Zhang think that the contradiction shows something deep and profound, whereas all it shows is their lack of in-depth knowledge of their subject matter. Halbach, along with Albert Visser, has also published two papers (Footnote: Volker Halbach & Albert Visser, Self-reference in Arithmetic 1 (PDF), Self-reference in Arithmetic 2 (PDF), Review of Symbolic Logic, 7(4), Part 1: 671-691, Part 2: 692-712 (2014)) in the Journal of Symbolic Logic that amount to forty-two pages, and which are supposed to be an authoritative review of self-reference. But throughout the papers Halbach and Visser simply assume that a formal language can self-reference - and even though the papers are meant to be a review of self-reference, there is no attempt at all to prove that such a self-reference can occur in a fully formal language. Unfortunately this is completely typical of the current approach of academic people who like to call themselves “logicians”, where an unprovable assumption has been elevated to a dogmatic mantra that no-one is allowed to question.

It is elementary to demonstrate that an enumeration of the formulas of a given language * L* can be achieved in a meta-language to the language

We assume that there is a enumeration of the formulas of a given language * L* within

*f*(123…) = *f*(*x*)

where **123…** is some specific numerical value. This, of course, is absurd, since now we have a non-variable term on the left side and a variable term on the right side. It follows that Halbach & Zhang’s claim that there can be a formula ** f** in the same language

This conclusion can also be adduced by considering the inverse of Halbach & Zhang’s purported mapping function, as follows:

If it is possible for the predicate * Sat* to evaluate from the values given to its variables, then it must be able to access the information contained in any constant that is purportedly given by the mapping

It is obvious that it is the assumption of an enumeration function within the language itself, and the resultant conflation of constant and variable terms, is the source of the contradiction that Halbach & Zhang remark upon in their article. It isn’t at all surprising that a conflation of constant and variable terms results in a contradiction, since the system that Halbach & Zhang have described is a system that is lacking the fundamental requirements of logical systems.

Halbach & Zhang say in their article that they *“hope to further our understanding of what the source
of the paradox is”*, and indicate their total bafflement at what is patently obvious. As demonstrated on the page Yablo’s paradox, it is child’s play to see what the source is. It is no surprise that the source is the same as in many similar paradoxes - the source is a self-reference engendered by vagueness of definition.

What is very surprising is that, while one can presume that referees for the journal Analysis examined Halbach & Zhang’s article, they appear to have simply accepted Halbach & Zhang’s assumptions without subjecting them to even the most basic sort of critical appraisal. But when there is an assumption to the effect that, although something is utilized within a proof it is not actually essential to the proof (such as Halbach & Zhang’s hypothetical function), that assumption should always be viewed with more than a modicum of suspicion.

Footnotes:

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There is now a new page Halbach and Zhang’s *Yablo without Gödel* which analyzes the illogical assumptions used by Halbach and Zhang.

I found that making, adding or deleting footnotes in the traditional manner proved to be a major pain. So I developed a different system for footnotes which makes inserting or changing footnotes a doddle. You can check it out at Easy Footnotes for Web Pages (Accessibility friendly).

I have now added a new section to my paper on Russell O’Connor’s claim of a computer verified incompleteness proof. This shows that the flaw in the proof arises from a reliance on definitions that include unacceptable assumptions - assumptions that are not actually checked by the computer code. See also the new page Representability.

There is now a new page on Chaitin’s Constant (Chaitin’s Omega), which demonstrates that Chaitin has failed to prove that it is actually algorithmically irreducible.

8 Apr 2016 Are we alone in the Universe?

13 May 2015 Good Math, Bad Math?

31 Mar 2015 Cranks and Crackpots

16th Mar 2015 Bishops Dancing with Pixies?

For convenience, there are now two pages on this site with links to various material relating to Gödel and the Incompleteness Theorem

– a page with general links:

– and a page relating specifically to the Gödel mind-machine debate:

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Copyright © James R Meyer 2012 - 2018

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