Translation guide
Expresses obligation or necessity. The most common pattern is 〜なければならない, but shorter forms like 〜なきゃ or 〜ないと are more natural in casual speech. The choice depends on formality and whether the obligation is personal or external.
Express that someone must do something, either by personal feeling or external rule.
Standard polite/written form. Attach to the negative stem of a verb (ない-form minus ない).
明日までにレポートを出さなければならない。
I have to submit the report by tomorrow.
Similar to 〜なければならない, slightly more subjective or personal. Often used in spoken Japanese.
もう行かなければいけない。
I have to go now.
Casual abbreviation of 〜ないといけない. Very common in everyday conversation. The ending いけない/ならない is often omitted.
そろそろ帰らないと。
I have to go home soon.
Very casual contraction of 〜なければ. Often used without いけない/ならない. Common among friends and family.
宿題やらなきゃ。
I have to do my homework.
Formal written equivalent of 〜なければならない. Often used in official documents or serious contexts.
規則を守らなくてはならない。
One must follow the rules.
Emphasize that there is no alternative but to do something, often with a negative nuance.
Formal expression meaning 'cannot help but do'. Attach to the negative stem of a verb (ない-form minus ない). The verb する becomes せざるを得ない.
その意見には反対せざるを得ない。
I have to disagree with that opinion.
Casual way to say 'there is nothing but to do'. Attach to the dictionary form of a verb.
やるしかない。
I have no choice but to do it.
Formal/literary equivalent of 〜しかない. Attach to dictionary form.
諦めるよりほかない。
There is no choice but to give up.
Express that something is not allowed or must not be done. Note: English 'have to' in negative becomes 'must not' in Japanese, not 'don't have to'.
Standard prohibition. Attach to て-form of verb.
ここで写真を撮ってはいけない。
You must not take photos here.
Formal/written prohibition, stronger than 〜てはいけない.
この情報を外部に漏らしてはならない。
This information must not be leaked outside.
Casual contraction of 〜てはいけない. Used in everyday speech.
触っちゃだめ！
Don't touch! (You must not touch!)
Express lack of obligation. Note: This is the opposite of 'have to', but often confused by learners.
Standard way to say 'don't have to'. Attach to negative stem (ない-form minus ない).
明日は来なくてもいいです。
You don't have to come tomorrow.
Politer than 〜なくてもいい. Often used in formal situations.
無理に参加しなくてかまいません。
You don't have to force yourself to participate.
In Japanese, 〜てはいけない means 'must not' (prohibition), while 〜なくてもいい means 'don't have to' (lack of obligation). English 'have to' in negative can be ambiguous, so be careful.
〜なければならない is standard and safe for most situations. 〜ないと and 〜なきゃ are casual and common in speech. 〜ざるを得ない is formal and implies no choice. Choose based on context.