Are these comments on "double negatives" appropriate

Question

In comments responding to https://ell.stackexchange.com/a/195429/91457 the question of double negatives was raised and discussed. In this comment user Foogod wrote:

"I don't promise nothing" actually is wrong (it's not just "sounds wrong"). It is actually ungrammatical, because it is a double-negative (which are pretty much never correct in English). "anything" is really the only correct option here.

I responded here that:

Double negatives can be perfectly acceptable in standard English. They are common in some dialects.

I followed this with a list of examples, and a list of authors who have used double negatives, and a link to the Wikipedia article and another source

The [response] was to deny that my examples were double negatives at all, and to reassert an absolute rule against them, as the poster understood the term:

almost none of your examples are actually double-negatives. First, "un"-prefixed adjectives, etc, or verbs like "disagree", are not negatives in a grammatical sense. Secondly, a double-negative occurs when somebody uses two negative terms but actually means a negative (instead of a positive) result, such as "don't promise nothing", which is logically inconsistent with what was said, and therefore wrong.

I posted a question over on ELU, which has gotten several comments, but no formal answers, as well as links to http://websites.umich.edu/~jlawler/CELS-Negation.pdf and https://english.stackexchange.com/q/20629/191178 which seem interesting.

I am also concerned by this commentwhere the poster writes:

people seem to have the silly notion that just because people use a construction in English that that automatically makes it correct, but that is not how grammar actually works. Yes, people do bend the rules all the time for various reasons but that does not mean that one should pretend they don't exist at all, especially when talking to those new to the language.

I am concerned by the degree of prescriptivism which that comment seems to embody and by the effect of such an attitude on learners, who seem often all too ready to expect prescriptivist rules to govern English. See Descriptivist versus prescriptivist approach in describing 'correct' and my answer to that question

I also believe that the definition of "double negative" that these comments use is simply incorrect, specifically is unduly limiting, and that text using, for example litotes is considered a form of double negative.

I invite comment.

Answer 1

You seem to be asking or making points about two separate issues here: 1) what a double negative is and whether they're correct in English; and 2) whether prescriptivist comments are acceptable in such a case.

Since this is Meta, I'm only going fully address the second, but I'll need to define what "double negative" means in the context of that thread. This comment you referenced sums it up: "a double-negative occurs when somebody uses two negative terms but actually means a negative (instead of a positive) result, such as "don't promise nothing".

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If some aspect of English is naturally used and understood by native English speakers in some variety of English, or for some specific purpose somewhere, and is not considered "marked" in that environment, then by definition, it is correct within that variety of English. Any statement that it is "bad English" is wrong, and in a learning environment like ours, needs to be corrected.

The comment I quoted above unfortunately continues: "...which is logically inconsistent with what was said, and therefore wrong". Logic is not what determines grammar rules -- it's usage. Usage often follows logical paths, but it's under no obligation to do so. For example, saying someone is "head over heels" should mean they're in some unnatural position, but having your head over your heels is the normal state of humans, and unremarkable. Logic would dictate that the expression "head over heels" in fact is always used incorrectly, and actually means someone who is perfectly normal. But it doesn't mean that, because usage is king.

THAT SAID, if an English learner is asking about double negatives, they need to understand that while their usage is natural and correct in many varieties of English, in every standard English (as in literary, academic or news reporting English) around the world, the usage of double negatives is marked. It sounds incorrect, and the people who use them sound uneducated. A learner must be advised of this so they don't go using double negatives in their master theses, thinking they're standard.

You said in a comment:

Double negatives can be perfectly acceptable in standard English. They are common in some dialects.

Be careful about conflating "standard", "common" and "perfectly acceptable". There's no standard variety of English where double negatives are correct, however common they might be heard, but there are non-standard varieties of English where double negatives are common and 100% natural, and therefore correct.

This principle applies to every correct (somewhere) but "marked" (elsewhere) aspect of English, including expressions like "irregardless" and "beg the question".

This principle does not apply to common misuses of words, like using "opportunistic" to mean "taking opportunities" or "toothsome" to mean "toothy", nor to common misspellings of terms like "should of", "do diligence", or "tow the line", because those mistakes stem from unfamiliarity with their correct usage in their environment, as opposed to a difference with standard usages outside their environment.