ない

From Old Japanese. The adjectivizing suffix appears to derive ultimately from ancient copula or stative verb ぬ (nu).

• ねえ (nē)
• ねー (nē)

ない (rōmaji -nai)

1. used to form derivative -i adjectives from other terms: having that quality, having that state; very much that quality or state

   切 (せつ)ない、幼 (いと)けない、ぎこちない

   setsunai, itokenai, gikochinai

   very moving, really young of manner, having clumsiness

From the 連体形 (rentaikei, “attributive form”) of Early Middle Japanese adjective 無し (nashi), with the medial /-k-/ falling out.

ない (-i inflection, rōmaji nai)

1. 無い: not, there is no, lack

   スプーンが無 (な)い。

   Supūn ga nai.

   There is no spoon.

2. (by extension) 亡い: passed away, dead

• This term is often spelled in hiragana.
• In public speech and written language, the irregular expressions ありません (arimasen) and ありませんでした (arimasen deshita) (past) are recommended instead of ないです (nai desu) and なかったです (nakatta desu).
• When used as an auxiliary adjective, follows the 連用形 (ren'yōkei, “continuative or stem form”) of -i adjectives ending in く (-ku), and the 連用形 (ren'yōkei, “continuative or stem form”) of -na adjectives and nominals ending in で (de). In either case a binding particle (係助詞) can be inserted between the ren'yōkei and the nai, but は (wa) is usually used for the latter. では (de wa) can be contracted to じゃ (ja)

  このパソコンは安 (やす)くない。

  Kono pasokon wa yasuku nai.

  This computer is not cheap.

  私 (わたし)は韓 (かん)国 (こく)語 (ご)は上 (じょう)手 (ず)ではありません。

  Watashi wa kankokugo wa jōzu de wa arimasen.

  I am not good at Korean.

First appears in texts from the late Muromachi period as an eastern-dialect term.

Various etymologies are supposed as:

• From ancient eastern-dialect negative ending なふ (nafu), but there is a sizable gap of time between the apparent disappearance of nafu and the emergence of nai.[1] 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 ぬ (nu), with the negative sense possibly originating from the 未然形 (mizenkei, “irrealis or incomplete form”) 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 Edo period, the auxiliary conjugated irregularly, including nanda instead of modern nakatta (past), and naikereba instead of modern nakereba (conditional).[1]
• Derived from the negative particle ぬ (nu).

• IPA^(key): [na̠i]
• In Tokyo accent, the accent of the verb construction depends on the suffixed verb:[2]
  • If the suffixed verb is accented, the accent falls on the final mora in the mizenkei stem. E.g. つく​る [tsùkúꜜrù] (Nakadaka) → つくら​ない [tsùkúráꜜnàì] (Nakadaka).
  • If the suffixed verb is non-accented, the result:
    • is non-accented if the suffix takes the following forms: ない (nai), ないと (nai to), ないつもりだ (nai tsumori da), ないはずだ (nai hazu da), ない場 (ば)合 (あい) (nai baai)
    • has an accent falling on the first mora of the suffix, viz. な [na], if the suffix takes the following forms: ないから (nai kara), ないか (nai ka), ないでしょう (nai deshō), ないで (nai de), ないの… (nai no…), ないし (nai shi), ないなら (nai nara), なくて (nakute), なかった (nakatta), なければ (nakereba)
    • has an accent falling later in patterns like ないこと… [náí kótóꜜ …], ないよう… [náí yóꜜò …], ないそう… [náí sóꜜò …], ないほう… [náí hóꜜò …], ないらしい [náí ráshíꜜì]
  • There are a few exceptions like 恐れ入る: おそ​れいる [òsóꜜrèìrù] (Nakadaka) → おそ​れいらない [òsóꜜrèìrànàì] (Nakadaka)

ない (rōmaji -nai)

1. (jodōshi) Used to form the negative of verbs: not, don't

   学 (がっ)校 (こう)に行 (い)かない。

   Gakkō ni ikanai.

   I don't go to school.

• Attaches to the 未然形 (mizenkei, “incomplete form”) of the verb. For 五段活用 (godan katsuyō, “quintigrade conjugation”, also known in English as “type 1”) verbs, this is the stem form ending in -a.
  • ない (-nai) is not formed on ある (aru, “to be, to exist”). The negative form of ある (aru) in the modern standard language is the adjective ない (nai), not *あらない (aranai). However, other negative suffixes do form on ある (aru), e.g. あらず (arazu), あらぬ (aranu), あらん (aran), あらへん (arahen).
• Generally, ません (masen) and ませんでした (masen deshita) (past) are the recommended formal negative endings, instead of the somewhat less formal ないです (nai desu) and なかったです (nakatta desu), 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 無い (nai) have mostly converged in modern usage. One distinction that is still maintained by some speakers appears when attaching そう (sō, “appears like, seems like”) or すぎる (sugiru, “too, too much, in excess”):
  • 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.

• (rare, archaic) ぬ (nu)
• (very casual or archaic and dialectal) ん (n)
• (Kansai) へん (hen)