Translation guide
Expresses obligation, necessity, or strong recommendation. Japanese uses several patterns depending on the source of obligation (rule, personal feeling, common sense) and the situation.
Expressing that something is required or must be done, often due to rules, duty, or circumstances.
Standard pattern for 'must' or 'have to'. Used for both personal and external obligations. Formal and widely applicable.
宿題をしなければならない。
I must do my homework.
I have to get up early tomorrow.
Similar to ～なければならない, but slightly more conversational. Implies 'must' or 'have to'.
もう行かなくてはいけない。
I have to go now.
Casual spoken form of ～なくてはいけない. Often shortened to ～ないと.
早く寝ないといけない。
I have to go to bed early.
Expresses 'should' or 'ought to', based on moral duty or common sense. Stronger sense of right/wrong than ～なければならない.
約束は守るべきだ。
You must keep your promises.
Expressing that something is forbidden or not allowed.
Standard pattern for 'must not' or 'may not'. Used in rules and instructions.
ここでタバコを吸ってはいけない。
You must not smoke here.
Formal, written form of prohibition. Often used in official documents.
この書類をなくしてはならない。
You must not lose this document.
Casual prohibition. Often used in speech, especially with children.
触っちゃだめ！
Don't touch!
Expressing that something is certainly the case, equivalent to 'must be' in English.
Expresses strong conviction or certainty. 'Must be' or 'no doubt'.
彼は疲れているに違いない。
He must be tired.
Expresses expectation based on reason or logic. 'Should be' or 'must be'.
彼はもう着いているはずだ。
He must have arrived by now.
Colloquial expression for 'it's obvious that' or 'must be'. Stronger and more subjective than ～に違いない.
そんなの嘘に決まっている。
That must be a lie.
～なければならない is used for obligations imposed by external circumstances or rules. ～べきだ is used for moral obligations or advice based on personal judgment. For example, 'You must wear a seatbelt' (law) uses ～なければならない, while 'You must be kind to others' (moral) uses ～べきだ.
シートベルトをしなければならない。
You must wear a seatbelt.
人に親切にするべきだ。
You must be kind to people.
There is no single Japanese word that directly translates 'must'. Using a dictionary form like ～なければならない is the standard way to express obligation. Avoid trying to translate 'must' word-for-word.