A double negative is a construction occurring when two forms of grammatical negation are used in the same sentence. This is typically used to convey a different shade of meaning from a strictly positive sentence ("You're not unattractive" vs "You're attractive"). Multiple negation is the more general term referring to the occurrence of more than one negative in a clause. In some languages, double negatives cancel one another and produce an affirmative; in other languages, doubled negatives intensify the negation. Languages where multiple negatives affirm each other are said to have negative concord or emphatic negation. Lithuanian, Portuguese, Persian, French, Russian, Polish, Bulgarian, Greek, Spanish, Icelandic, Old English, Italian, Afrikaans, and Hebrew are examples of negative-concord languages. This is also true of many vernacular dialects of modern English. Chinese, Latin, German (with some exceptions in various High German dialects), Dutch, Japanese, Swedish and modern Standard English are examples of languages that do not have negative concord. Typologically, negative concord occurs in a minority of languages.

Languages without negative concord typically have negative polarity items that are used in place of additional negatives when another negating word already occurs. Examples are "ever", "anything" and "anyone" in the sentence "I haven't ever owed anything to anyone" (cf. "I haven't never owed nothing to no one" in negative-concord dialects of English, and "Nunca devi nada a ninguém" in Portuguese, lit. "Never have I owed nothing to no one", "Non ho mai dovuto nulla a nessuno" in Italian, or "Nigdy nikomu niczego nie zawdzięczałem" in Polish). Negative polarity can be triggered not only by direct negatives such as "not" or "never", but also by words such as "doubt" or "hardly" ("I doubt he has ever owed anything to anyone" or "He has hardly ever owed anything to anyone").

Because standard English does not have negative concord but many varieties and registers of English do, and because most English speakers can speak or comprehend across varieties and registers, double negatives as collocations are functionally auto-antonymic (contranymic) in English; for example, a collocation such as "ain't nothin" or "not nothing" can mean either "something" or "nothing", and its disambiguation is resolved via the contexts of register, variety, location, and content of ideas.

Stylistically, in English, double negatives can sometimes be used for affirmation (e.g. "I'm not feeling unwell"), an understatement of the positive ("I'm feeling well"). The rhetorical term for this is litotes.

When two negatives are used in one independent clause, in standard English the negatives are understood to cancel one another and produce a weakened affirmative (see the Robert Lowth citation below): this is known as litotes. However, depending on how such a sentence is constructed, in some dialects if a verb or adverb is in between two negatives then the latter negative is assumed to be intensifying the former thus adding weight or feeling to the negative clause of the sentence. For this reason, it is difficult to portray double negatives in writing as the level of intonation to add weight in one's speech is lost. A double negative intensifier does not necessarily require the prescribed steps, and can easily be ascertained by the mood or intonation of the speaker. Compare

versus

These two sentences would be different in how they are communicated by speech. Any assumption would be correct, and the first sentence can be just as right or wrong in intensifying a negative as it is in cancelling it out; thereby rendering the sentence's meaning ambiguous. Since there is no adverb or verb to support the latter negative, the usage here is ambiguous and lies totally on the context behind the sentence. In light of punctuation, the second sentence can be viewed as the intensifier; and the former being a statement thus an admonishment.

In Standard English, two negatives are understood to resolve to a positive. This rule was observed as early as 1762, when Bishop Robert Lowth wrote A Short Introduction to English Grammar with Critical Notes. For instance, "I don't disagree" could mean "I certainly agree", "I agree", "I sort of agree", "I don't understand your point of view (POV)", "I have no opinion", and so on; it is a form of "weasel words". Further statements are necessary to resolve which particular meaning was intended.