I have heard several sentences in which there was a prominent double negative, but the double negative "sounded right". Is this ever true, or is it just a misleading feeling?
Edited to include an example:
"Did you enjoy the movie?"
"Well, I didn't not enjoy it, but..."
I suppose that may just be bad grammar, but sometimes it seems to be the quickest way to say it.
Double negatives can be perfectly fine in English.
1.) I don't see nothing. (= I don't see anything.)
2.) I suppose that is not impossible. However, it seems far fetched.
Here the double negative expresses a weak positive, a very common construction.
3.) Not bad, not bad at all! You have just saved her life, young man.
This is a figure of speech called litotes: the double negative (if that's what it is) is used to express a strong positive. Sometimes any double negative with a positive meaning is considered a litotes, including the unremarkable example 2 above. Other people restrict the term to those negations that express a strong positive through an apparently weak positive, in a mildly ironical manner, as in this example (3).
4.) Never a day goes by that I do not miss her. (= I always miss her.)
This is the rhetorical double negative, often considered a form of litotes. It expresses a strong positive, though without irony.
5.) Well, I didn't not enjoy it, but...
Here the word not is used twice, once in contracted form (don't) and once in full, to express a weak positive. Double not is a special case: it is felt to be even more redundant than other double negatives and sounds rather colloquial. The majority will probably use this in speech and informal writing, where it is perfectly acceptable, but not elsewhere.
The boundary between negations and other kinds of words is by no means sharp. The prefixes un- and im-/in- are usually considered negatives, as are hardly and many others; bad is sometimes considered a negative word, sometimes not, etc.
There are two types of double negative, and I think it is important to recognize the difference between the two. They are:
It's not that I didn't enjoy it...
or:
I'm not unhappy/dishonest.
or:
When I see someone in trouble, I can't not help.
I think everyone would agree that these are common Standard English constructions.
(However, as I said, even your awkward example is not ungrammatical in Standard English.)
Side note: even negative concord exists in Standard English in certain cases. For example, in response to negative questions:
"You're not coming?" — "No (I'm not)."
Essentially, when someone asks a negative question, the answer of "no" does not yield the positive, i.e. it does not mean "No, I am coming". Instead, "no" creates negative concord, maintaining the negation of the question.
In other languages where they don't employ this negative concord, like Japanese for example, the way to respond to "you're not coming" would be "yes, I am not coming". Answering "no" would would mean "I am coming".
Most use of double negatives is indeed non-standard. But OP's example itself, although a little contrived, does show that the construct can be used quite correctly.
As this NGram shows, "[someone] can't not do [something]" is often used quite properly in non-contrived contexts. In short, the stricture against double negatives is not an absolute; it just so happens that many usages are in fact 'incorrect', particularly when repetition is simply being used to amplify the force of a statement.
Double negatives that express a negative statement are used in dialect, and non-standard usage.
In Old and Middle English double negatives were normal, and started to get "disapproved" since the 16th century.
It's non-standard.
At least in standard English.
In standard English, it is grammatically incorrect.
They used to be correct, i.e. in Shakespeare's day, it was considered emphatic(example: "He is not an unpleasant man" meaning he is a very pleasant man), but nowadays, with the change of English, it is now considered non-standard.
It is still used in certain dialects or slang and colloquialism, i.e. Ebonics, but it is considered non-standard.
The double negative seems to be also a standard element of bureaucratese. Government is called to action, to do something, but can't be too specific because it may not be motivated and might just be stalling for some quiet time. The double negative cannot stand for a design goal because it does not accept the accountability of a working design based upon a specific positive purpose defined with concrete language.
