なくてはいけない
Must do, Have to do
Structure
Verb［
Explanation
While it shares a similar structure with てはいけない, the grammar point なくてはいけない expresses the complete opposite. It's a classic example of a double negative, where two 'nots' cancel each other out to create a strong sense of obligation, meaning that something 'must be done'.
This structure is typically translated as 'must do', but its literal meaning is closer to 'it is not okay to not do (A)'. Understanding this double negative is key. The final part, いけない, means 'not good' or 'won't do', derived from the negative potential form of the verb 行く (to go).
To form this grammar point, take the negative form of any verb ending in ない. Change the final い to く, which is the standard conjunctive form for い-Adjectives. Then, simply attach てはいけない to the end.
- 宿題がたくさんあるから、今夜は勉強しなくてはいけない。I have a lot of homework, so I have to study tonight. (It's not okay to not do it)
- 図書館に本を返さなくてはいけない。I must return the book to the library. (It's not okay to not do it)
- 会議が始まる前に、このレポートを読まなくてはいけない。I have to read this report before the meeting starts. (It's not okay to not do it)
Of the various ways to express 'must do', いけない is the most versatile and widely used in both spoken and written contexts. For more formal situations or written language, ならない is a suitable alternative. On the other hand, だめ is a more casual option used in informal conversations.
- 会社に着いたら、社長に報告しなくてはならない。When I get to the office, I must report to the president.
- 約束の時間に遅れなくてはダメだよ。You really mustn't be late for our appointment.
Caution
In casual speech, なくては is frequently shortened to なくちゃ for ease of pronunciation. This contracted form, なくちゃ, can be used by itself or followed by いけない, with no change in its 'have to' meaning.
- もうこんな時間だ。はやく帰らなくちゃいけない。Wow, it's this late already? I gotta head home.
- あっ、牛乳がない！買ってこなくちゃ。Oh no, we're out of milk! I've gotta go buy some.
This informal contraction is similar to how 'have to' becomes 'gotta' in casual English.
Examples
明日までに図書館に本を返さなくてはいけない。
I have to return this book to the library by tomorrow.
頭が痛いから、薬を飲まなくてはいけない。
Because I have a headache, I have to take some medicine.
友達が遊びに来るから、部屋をそうじしなくてはいけない。
My friends are coming over, so I have to clean my room.
もうすぐ飛行機に乗るので、スマホの電源を切らなくてはいけない。
I'll be boarding the plane soon, so I must turn off my phone.
締め切りは今日だから、レポートを出さなくてはいけない。
The deadline is today, so I have to submit my report.
明日は大事な会議があるので、早く起きなくてはいけない。
I have an important meeting tomorrow, so I have to get up early.
雨が降ってきたから、洗濯物を取り込まなくてはいけない。
It started raining, so I have to bring in the laundry.
犬の散歩の時間だから、そろそろ出かけなくてはいけない。
It's time to walk the dog, so I have to go out soon.
パスポートの有効期限がもうすぐ切れるので、更新しなくてはいけない。
My passport is going to expire soon, so I have to renew it.
お金がないから、銀行に行かなくてはいけない。
I don't have any money, so I have to go to the bank.
映画がもうすぐ始まるから、席に座らなくてはいけない。
The movie is about to start, so we have to sit down in our seats.
部屋を出るときは、電気を消さなくてはいけない。
When you leave a room, you must turn off the lights.