ない

Etymology 1
From. The adjectivizing suffix appears to derive ultimately from ancient copula or stative verb.

Suffix

 * : having that quality, having that state; very much that quality or state

Derived terms

 * : dangerous
 * , : young; immature, childish
 * : clumsy, awkward
 * : very moving, especially in a sad or poignant way; painful in an emotional way; hard to breathe, especially from strong emotions
 * : low, vulgar, rude
 * : fidgety, restless, in a rush
 * : good-for-nothing, disappointing, timid, shameful, useless

Adjective

 * 1)  no, not any
 * 2) not reaching a certain quantity; less than
 * 3)   passed away, dead
 * 1)   passed away, dead
 * 1)   passed away, dead

Usage notes

 * In public speech and written language, the irregular expressions and  (past) are recommended instead of  and.
 * When used as an auxiliary adjective, it follows:
 * the of -i adjectives, which ends in ;
 * and the of -na adjectives and nominals, which ends in.
 * In either case a binding particle can be inserted between the ren'yōkei and the nai, but  is usually used for the latter. The resulting  can be contracted to.
 * In Kansai dialect, the of -i adjectives can be absent.
 * In either case a binding particle can be inserted between the ren'yōkei and the nai, but  is usually used for the latter. The resulting  can be contracted to.
 * In Kansai dialect, the of -i adjectives can be absent.
 * In Kansai dialect, the of -i adjectives can be absent.

Inflection

 * When with the suffix, it is  instead of.

Etymology 3
First appears in texts from the late as an eastern-dialect term.

Various etymologies are supposed as:
 * From ancient eastern-dialect negative ending, but there is a sizable gap of time between the apparent disappearance of nafu and the emergence of nai. Moreover, nafu conjugated as a verb, whereas nai conjugates as an adjective.
 * That said, both nafu and nai probably derive ultimately from ancient copula or stative verb, with the negative sense possibly originating from the of the verb stem, to which these endings attach.


 * From the adjective ない (etymology 2). The nai auxiliary conjugates as a regular -i adjective just like the adjective nai in modern Japanese, but the patterns for the auxiliary were originally different from the adjective. In the, the auxiliary conjugated irregularly, including nanda instead of modern nakatta (past), and naikereba instead of modern nakereba (conditional).
 * Derived from the negative suffix.

Pronunciation

 * In Tokyo accent, the accent of the verb construction depends on the suffixed verb:
 * If the suffixed verb is accented, the accent falls on the final mora in the mizenkei stem. E.g. →.
 * If the suffixed verb is non-accented, the result:
 * is non-accented if the suffix takes the following forms:, , , ,
 * has an accent falling on the first mora of the suffix, viz. な, if the suffix takes the following forms: , , , , , , , , ,
 * has an accent falling later in patterns like ないこと…, ないよう… , ないそう… , ないほう… , ないらしい
 * There are a few exceptions like : →

Suffix

 * 1)  not, don't

Usage notes

 * Attaches to the of the verb.  For  verbs, this is the stem form ending in -a.
 * is not formed on . The negative form of in the modern standard language is the adjective, not . However, other negative suffixes do form on , e.g. , , ,.
 * This word is morphologically an inflectional suffix. It is classified as in traditional Japanese grammar.
 * Generally, and  (past) are the recommended formal negative endings, instead of the somewhat less formal  and, which are considered incorrect by conservative speakers. The original incompatibility of ない and です may be explained by the origin of ない as a verb, cf. the Etymology section.
 * The auxiliary nai and the adjective have mostly converged in modern usage.  One distinction that is still maintained by some speakers appears when attaching  or :
 * Adjective nai + sō or sugiru → nasasō, nasasugiru
 * Auxiliary nai + sō or sugiru → nasō, nasugiru
 * The process of convergence is ongoing, and the さ-infix might be used by some speakers even with the auxiliary. This could be considered as proscribed in formal contexts, as slang or a grammatical error.