modality N5 essential casualpolitewritten
なくてはいけない — must ~
なくてはいけない
Builds on なくては
Meaning
- must ~ / have to ~ — an obligation, framed as 'if I don't do it, it won't do'
Key sentence
毎日薬を飲まなくてはいけない。
I have to take medicine every day.
Formation
| Attaches to | Form | Example |
|---|---|---|
| Verb (ない-form, drop い) | V-なく + てはいけない | 飲む → 飲まない → 飲まなくてはいけない |
| Noun / na-adjective | N/na-adj + でなくてはいけない | 18歳以上でなくてはいけない |
Variants
なくちゃ（いけない） — casual contraction of なくては → なくちゃ; the いけない is often dropped: 行かなくちゃ ('gotta go').
Examples
明日は早く起きなくてはいけません。
I have to get up early tomorrow.
図書館の本は来週までに返さなくてはいけない。
I have to return the library books by next week.
ここでは静かにしなくてはいけない。
You have to be quiet here.
Easily confused with
〜なくてはならない Same meaning; いけない feels personal / situation-specific, ならない states a general rule or social/moral obligation and sounds more formal. 〜なければならない Identical meaning, different base: なくては is a bit more conversational, なければ slightly more formal/written. 〜なくてもいい Opposites: なくてはいけない = 'must do'; なくてもいい = 'don't have to do'.
See なくてはいけない in real sentences
Jengo shows なくてはいけない the way you actually meet it: inside real Japanese sentences, so it sticks instead of staying an abstract rule.
Study it in JengoSources Compiled with reference to A Dictionary of Basic Japanese Grammar.