1.
must; have to; cannot do otherwise
A grammatical pattern expressing necessity or obligation. Attaches to the negative stem of verbs and to nouns/na-adjectives via で. Literally "if (it is) not so, it will not do," but used straightforwardly to mean "must."
Formed from the negative stem (e.g. 行か-) + ければならない. Conveys obligation, requirement, or unavoidable necessity. Typically a written or polite-spoken form; in casual conversation it is often shortened.
Forms
- Verbs: drop the final い of the plain negative and add ければならない (食べない → 食べなければならない)
- I-adjectives: drop the final い and add くなければならない (若い → 若くなければならない)
- Nouns / Na-adjectives: + でなければならない
- なければ → なきゃ (食べなきゃ — gotta eat)
- なければならない → なきゃならない / なきゃいけない / なきゃ
Similar words
- なくてはならない: also "must" — slightly more formal feel; nearly interchangeable
- なくてはいけない: "must" — common in spoken Japanese
- ねばならない: "must" — literary/written register
Register
The full form なければならない sounds careful and is common in writing, announcements, and explanations of rules. In everyday conversation, contractions are far more frequent.