なくてはいけない details
write + must do
kaka nakute wa ikenai
must do; have to do
meaning: have to write
もう遅いから寝なくちゃ。
mou osoi kara nenakucha.
It's late — I've gotta get to bed. casual
来週までにビザを更新しなくてはいけない。
raishuu made ni biza o koushinshi nakute wa ikenai.
I have to renew my visa by next week. neutral
- contraction
- colloquial
- formal
- past
- polite
Examples
must do; have to — stating an obligation
もう遅いから寝なくちゃ。
mou osoi kara nenakucha.
It's late — I've gotta get to bed. casual
来週までにビザを更新しなくてはいけない。
raishuu made ni biza o koushinshinakutehaikenai.
I have to renew my visa by next week. neutral
会員は年会費を納めなくてはなりません。
kaiin wa nenkaihi o osamenakute wa narimasen.
Members must pay the annual fee. formal
Formation
{V-nai-stem}なくてはいけないattaches to ない-stem
Variant notes
- なくちゃ — なくては→なくちゃ in speech, tail usually dropped — 早[はや]く寝[ね]なくちゃ。
- なくちゃいけない — contracted front with the tail kept — the usual full spoken form
- なくてはならない — written necessity — rules, requirements, exam prose; parallels てはならない
Related patterns
Similar
Same obligation, same いけない tail — ないと is the everyday spoken default, while なくては carries more weight and turns up more in writing and careful speech.
Lookalikes
Both mandate the same act and share the ならない/いけない tails; only the fronts differ, and blending them at recall speed yields non-words like なくれば — learn なければ and なくては as unsplittable wholes.
Shared てはいけない tail, opposite forces — てはいけない forbids the act, なくてはいけない mandates it; the なく in front flips prohibition into obligation.