Talk:Validity (logic)

Validity of statements?
I removed the section on the "validity of statements." I have never seen a logic textbook that referred to statements of any kind as "valid," and to do so in an encyclopedia article seems confusing. There were no sources cited. The section wrongfully conflated validity with "logical truth" (whatever that is). And the example that it gave was just a tautology ("if no god is mortal, then no mortal is god"). Brijohn6882 (talk) 20:57, 6 January 2012 (UTC)


 * Someone has replaced part of the original section, but it's inaccurate, so I'm going to remove it. It currently reads: "A statement can be called valid, i.e. logical truth, if it is true in all interpretations." I know of no logic textbook that refers to statements as valid or invalid, in this sense or any other. "Validity" is used in Logic to denote when a conclusion necessarily follows from a set of premises (note the distinction between Validity and Soundness). Statements are judged as being "true" or "false" not "valid" or "invalid." In addition, it is not clear at all what "logical truth" means in this passage. I would add that "can be called" is a Weasley in this context, because anything "can be called" by any name. The purpose of an encyclopedia article about Validity is to tell readers how the word is typically used. In Philosophy, and in Logic specifically, "Validity" is not used to describe statements, only arguments. There could be a section about the way validity is used in other contexts, but this section is clearly out of place.Brijohn6882 (talk) 22:21, 6 January 2012 (UTC)


 * Try Quine, Philosophy of logic. "Validity" of all of these entities is mentioned in the literature, and it is a good idea to cover all of the varying useages. Wikipedia articles are supposed to be comprehensive.Greg Bard (talk) 22:55, 6 January 2012 (UTC)


 * I stand corrected. Quine's "Philosophy of Logic" definitely does talk about statements as being valid in Chapter 4, Logical Truth. He talks about the validity of "schema," but it's clear that, as he uses the term, "validity" could be applied to statements with inferential content (for example, "if, then" statements). What I do think is crucial -- and ought to be made clear in a wikipedia article -- is that all statements that can be described as valid have a some sort of inferential content, such that they could be rewritten as valid arguments (so a valid "if, then" statement would be one in which the then clause followed necessarily from the if clause, which explains why the original example was a tautology). I will be thinking of ways to make this clear in hopes of improving the article. Also, I will add a link to the wikipedia article on Logical Truth. Please forgive the clumsiness of my original edit. Brijohn6882 (talk) 22:01, 22 January 2012 (UTC)

Naming the disambiguation page
This article was originally entitled Validity (disambiguation), whcih is surley a better name for it. Any objections or reason against moving it back to Validity (disambiguation)? --Philogo (talk) 13:32, 3 February 2009 (UTC)
 * Disambiguation Zero sharp (talk) 16:59, 3 February 2009 (UTC)

Add Link to Test_validity?
Does anyone object to adding a link to Test_validity? Jmbrowne (talk) 03:14, 14 February 2009 (UTC)
 * No objections, so I made the change. Jmbrowne (talk) 20:01, 16 February 2009 (UTC)

Validity of statements meaningless?
I reverted a statement to the effect that only arguments can be valid, statements being only true or false. This is subject to definition and convention. I do not claim that the claim is unacceptable in principle, but if it is to earn its place in the article, the underlying principles and conventions need to be made explicit together with proper citation. It could be argued for example that a statement that is necessarily true/false/meaningless/contingent, is correspondingly valid/invalid. If this argument is rejected, it first must be made clear what conventions from which authorities forbid them. It also must be made clear which restatements of such a statement would be acceptable in asserting its (in)validity.

Eg: X= not(X) cannot be true for any relevant, meaningful and meaningfully compatible classes of values for X, "=" and "not (X)". Conversely for X=X. X=Y would be contingent, and =X= would be meaningless in most conventions. To call some of those forms of statements valid according to some conventions would be sufficiently defensible, for denial of its permissibility to require appropriate explanation and supporting citation. To argue that such a statement amounts to a 1-statement argument, which is why it is (in)valid, might be defensible, but then we need a far less natural definition of "statement" and "argument" to accommodate the argument, still together with adequate relevant citation. JonRichfield (talk) 15:27, 6 December 2012 (UTC)

examples
i can't find an example of an invalid syllogism on this page. I would appreciate an example of one where the premises are true but it is still invalid. 69.125.59.43 (talk) 21:07, 13 December 2013 (UTC)
 * How about:
 * All chimpanzees are mortal.
 * All apes are mortal.
 * Therefore, all chimpanzees are apes.
 * There you have an invalid syllogism with true premises and a true conclusion. Dezaxa (talk) 22:57, 27 March 2015 (UTC)


 * To be more precise: logical arguments must not violate the rules of deductive reasoning of the formal system. The example above does violate those said rules. That's why it is indeed invalid. Fabio Maria De Francesco (talk) 07:30, 8 December 2019 (UTC)

Ω-validity
Please see discussion at WT:WPM. --Trovatore (talk) 19:23, 1 July 2017 (UTC)

Restoration of page histories
At present the page Validity (disambiguation) lists sixteen uses of the word "validity". Of those, the technical meaning in logic is given the article title Validity. It does not seem to me that that one meaning is in any sense a primary meaning of the word, and so I was considering moving Validity to Validity (logic) and Validity (disambiguation) to Validity. However, rather than just rush into doing so I first checked the history of the pages, to see whether there was anything there indicating a reason not to do so. I found that until the arrangement I had in mind was in fact exactly what had existed until February 2009. At that time not only did one editor unilaterally change the situation without either discussing the matter or even explaining his reason, but more importantly he did so by improperly copying content from pages and pasting them into others, losing the editing history and failing to give attribution. I am therefore intending to do a history swap and merge, restoring the history and titles of the pages involved. The editor who uses the pseudonym "JamesBWatson" (talk) 10:18, 28 August 2018 (UTC)
 * Done. The editor who uses the pseudonym "JamesBWatson" (talk) 11:46, 28 August 2018 (UTC)