Grammar › Obligation › 〜なくてはいけない
〜なくてはいけない
"I have to." Japanese builds "must" out of a double negative — literally "not doing it won't do" — and then squashes it into なくちゃ, なきゃ, ないと in real speech.
The short version
Take the verb's negative stem (行か-, 食べ-) and finish with "…won't do": なくては or なければ, plus いけない / ならない. It reads as a double negative but simply means "must / have to". The final いけない/ならない is often dropped once the meaning is clear.
行く → 行かなくてはいけない — have to go
行かなければならない ／ 行かないと — same meaning
〜なくてはいけない — the full form
The textbook shape, common in careful or polite speech.
何かを食べなくてはいけない。
You have to eat something. (食べない + なくては + いけない)
How it's really said — なきゃ / なくちゃ / ないと
Almost nobody says the full form in casual talk. It collapses:
| Full form | Casual | Meaning |
|---|---|---|
| なくては | なくちゃ | gotta |
| なければ | なきゃ | gotta |
| ないといけない | ないと | gotta (trailing off) |
これは不良の歯だから早く抜かなくちゃ。
This is a bad tooth, so I've gotta pull it out soon. (なくては → なくちゃ)
選挙に行かないと。
I've gotta go vote. (ないといけない → ないと)
Watch out
Two negatives, one obligation. The なく / なけれ is a negative, and いけない/ならない is another — together they cancel into a positive "must". Trailing なきゃ/なくちゃ/ないと all mean "gotta…", with the rest left unsaid.
Next: 〜なくてもいい — don't have to → · 〜てはいけない → · All grammar
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