In Indo-European languages, it is not customary to speak of a negative mood, since in the 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. 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.