Grammatical polarity is the distinction of affirmative and negative. In English, grammatical polarity is generally indicated by the presence or absence of the modifier not, which negates the statement. Many other languages contain similar modifiers: Italian and Interlingua have non, Spanish has no, French has ne ... pas, Esperanto has ne, German has nicht, and Swedish has inte. Special negative and affirmative items are often found in answers to questions. In English, these are no and yes respectively, in French non and oui, and Swedish nej and ja. In addition to this, some languages have a distinct form for a positive answer to a negative question, such as French si and Swedish jo.
In many languages, rather than inflecting the verb, negation is expressed by adding a particle:
Standard English adds the word not after the auxiliary verb and before the main verb; if no auxiliary verb is present, the dummy auxiliary do (so named because of its zero semantic content) is inserted. For example, "I must go" is negated as "I must not go", and "I go" is negated as "I do not go". In the third person singular, do is inflected as does: "He does not go."
In Indo-European languages, it is not customary to speak of a negative mood, since in these languages negation is originally a grammatical particle that can be applied to a verb in any of these moods. Nevertheless, in some, like Welsh, verbs have special inflections to be used in negative clauses.
In other language families, the negative may count as a separate mood. An example is Japanese, which conjugates verbs in the negative after adding the suffix -nai (indicating negation), e.g. tabeta ("ate") and tabenakatta ("did not eat"). It could be argued that Modern English has joined the ranks of these languages, since negation in the indicative mood requires the use of an auxiliary verb and a distinct syntax in most cases. Zwicky and Pullum have shown that n't is an inflectional suffix, not a clitic or a derivational suffix.[1] Contrast, for instance, "He sings" → "He doesn't sing" (where the dummy auxiliary do has to be supplied and inflected to doesn't) with Il chante → Il ne chante pas; French adds the (discontinuous) negative particle ne ... pas, without changing the form of the verb.