In linguistics and grammar, affirmation and negation (abbreviated respectively AFF and NEG) are the ways that grammar encodes negative and positive polarity in verb phrases, clauses, or other utterances. Essentially an affirmative (positive) form is used to express the validity or truth of a basic assertion, while a negative form expresses its falsity. Examples are the sentences "Jane is here" and "Jane is not here"; the first is affirmative, while the second is negative.
The grammatical category associated and with affirmative and negative is called polarity. This means that a sentence, verb phrase, etc. may be said to have either affirmative or negative polarity (its polarity may be either affirmative or negative). Affirmative is typically the unmarked polarity, whereas a negative statement is marked in some way, whether by a negating word or particle such as English not, an affix such as Japanese -nai, or by other means, which reverses the meaning of the predicate. The process of converting affirmative to negative is called negation - the grammatical rules for negation vary from language to language, and a given language may have more than one method of doing so.
Affirmative and negative responses (especially, though not exclusively, to questions) are often expressed using particles or words such as yes and no, where yes is the affirmative and no the negative particle.
Special affirmative and negative words (particles) are often found in responses to questions, and sometimes to other assertions by way of agreement or disagreement. In English, these are yes and no respectively, in French oui, si and non, in Swedish ja, jo and nej, and so on. Not all languages make such common use of particles of this type; in some (such as Welsh) it is more common to repeat the verb or another part of the predicate, with or without negation accordingly.
Complications sometimes arise in the case of responses to negative statements or questions; in some cases the response that confirms a negative statement is the negative particle (as in English: "You're not going out? No."), but in some languages this is reversed. Some languages have a distinct form to answer a negative question, such as French si and Swedish jo (these serve to contradict the negative statement suggested by the first speaker).
Other examples of negating particles preceding the verb phrase include Italian non, Russian nye and Polish nie (they can also be found in constructed languages: ne in Esperanto and non in Interlingua). In some other languages the negating particle follows the verb or verb phrase, as in Dutch:
Particles following the verb in this way include not in archaic and dialectal English ("you remember not"), nicht in German (ich schlafe nicht, "I am not sleeping"), and inte in Swedish (han hoppade inte, "he did not jump").
In French, particles are added both before the verb phrase (ne) and after the verb (pas):
However, in colloquial French the first particle is often omitted: Je sais pas. Similar use of two negating particles can also be found in Afrikaans: Hy kan nie Afrikaans praat nie ("He cannot speak Afrikaans").
In standard Modern English, negation is achieved by adding not after an auxiliary verb (which here means one of a special grammatical class of verbs that also includes forms of the copula be; see English auxiliaries). If no such verb is present then the dummy auxiliary do (does, did) is introduced - see do-support. For example:
Different rules apply in subjunctive, imperative and non-finite clauses. For more details see English grammar § Negation. (In Middle English, the particle not could follow any verb, e.g. "I see not the horse.")
In some languages, like Welsh, verbs have special inflections to be used in negative clauses. (In some language families, this may lead to reference to a negative mood.) An example is Japanese, which conjugates verbs in the negative after adding the suffix -nai (indicating negation), e.g. taberu ("eat") and tabenai ("do not eat"). It could be argued that English has joined the ranks of these languages, since negation requires the use of an auxiliary verb and a distinct syntax in most cases; the form of the basic verb can change on negation, as in "he sings" vs. "he doesn't sing". Zwicky and Pullum have shown that n't is an inflectional suffix, not a clitic or a derivational suffix.
Complex rules for negation also apply in Finnish; see Finnish grammar § Negation of verbs. In some languages negation may also affect the dependents of the verb; for example in some Slavic languages, such as Polish, the case of a direct object often changes from accusative to genitive when the verb is negated.
Negation can be applied not just to whole verb phrases, clauses or sentences, but also to specific elements (such as adjectives and noun phrases) within sentences. Ways in which this can be done again depend on the grammar of the language in question. English generally places not before the negated element, as in "I witnessed not a debate, but a war." There are also negating affixes, such as the English prefixes non-, un-, in-, etc. Such elements are called privatives.
There also exist elements which carry a specialized negative meaning, including pronouns such as nobody, none and nothing, determiners such as no (as in "no apples"), and adverbs such as never, no longer and nowhere.
Although such elements themselves have negative force, in some languages a clause in which they appear is additionally marked for ordinary negation. For example, in Russian, "I see nobody" is expressed as ? ? ja nikovó nye vízhu, literally "I nobody not see" - the ordinary negating particle nye ("not") is used in addition to the negative pronoun ? nikovó ("nobody"). Italian behaves in a similar way: Non ti vede nessuno, "nobody can see you", although Nessuno ti vede is also a possible clause with exactly the same meaning.
In Russian, all of the elements ("not", "never", "nobody", "nowhere") would appear together in the sentence in their negative form. In Italian, a clause works much as in Russian, but non does not have to be there, and can be there only before the verb if it precedes all other negative elements: Tu non porti mai nessuno da nessuna parte. "Nobody ever brings you anything here", however, could be translated Nessuno qui ti porta mai niente or Qui non ti porta mai niente nessuno. In French, where simple negation is performed using ne ... pas (see above), specialized negatives appear in combination with the first particle (ne), but pas is omitted:
In Ancient Greek, a simple negative ( ou "not" or m? "not (modal)") following another simple or compound negative (e.g. oudeís "nobody") results in an affirmation, whereas a compound negative following a simple or compound negative strengthens the negation:
Simple grammatical negation of a clause in principle has the effect of converting a proposition to its logical negation - replacing an assertion that something is the case by an assertion that it is not the case.
In some cases, however, particularly when a particular modality is expressed, the semantic effect of negation may be somewhat different. For example, in English, the meaning of "you must not go" is not in fact the exact negation of that of "you must go" - this would be expressed as "you don't have to go" or "you needn't go". The negation "must not" has a stronger meaning (the effect is to apply the logical negation to the following infinitive rather than to the full clause with must). For more details and other similar cases, see the relevant sections of English modal verbs.
Negation flips downward entailing and upward entailing statements within the scope of the negation. For example, changing "one could have seen anything" to "no one could have seen anything" changes the meaning of the last word from "anything" to "nothing".
For the use of double negations or similar as understatements ("not unappealing", "not bad", etc.) see litotes.