～ない
plain negative auxiliary
～ない is the plain negative of verbs: 食べる (to eat) becomes 食べない (do not eat). It is the casual counterpart of polite ～ません, and it covers both present and future: “don’t” and “won’t”.
1. Saying what you do not (or will not) do
Attach ない to the negative stem of the verb. Words like 何も (nothing) need a negative verb to complete their meaning.
今日は何も食べない。
“I’m not eating anything today.”
- 今日（きょう）= today
- は = topic marker
- 何も（なにも）= nothing, (not) anything
- 食べない（たべない）= will not eat, am not eating
2. ない conjugates like an i-adjective
Once a verb is in the ない-form, the ending behaves like an i-adjective: the past is ～なかった (did not), and the て-form is ～なくて.
昨日は勉強しなかった。
“I didn’t study yesterday.”
- 昨日（きのう）= yesterday
- は = topic marker
- 勉強しなかった（べんきょうしなかった）= did not study (past of 勉強しない)
How to form it
う-verbs: change the final -u to -a + ない (verbs ending in う take わ: 買う → 買わない). る-verbs: drop る + ない. Irregular: する → しない, 来る → 来ない.
- 書く（かく）= to write → 書かない（かかない）= do not write
- 食べる（たべる）= to eat → 食べない（たべない）= do not eat
- 来る（くる）= to come → 来ない（こない）= do not come
Key idea
ない is the plain “not” of Japanese. Attach it to the negative stem, and remember that from then on it conjugates like an i-adjective — so “didn’t” is なかった, not a new verb form.
Built on the same stem
Updated .