でなければならない

also: でなければいけない · でなければならぬ

Meanings

must be; have to be; ought to be

Used after a noun or na-adjective stem with で to state a required identity, status, quality, or condition. It is the copular counterpart of なければならない: literally, 'if it is not ..., it will not do.'

See also: である · なければならない

リーダーは常つねに冷れい静せいでなければならない。
A leader must always be calm.
申しん請せい者しゃは十じゅう八はっ歳さい以い上じょうでなければいけない。
Applicants must be at least eighteen years old.
指し導どう者しゃは公こう正せいでなければならぬ。
A leader must be fair.

Related words

なければならない
なければならない is the general 'must/have to' pattern used after verbs and adjectives, while でなければならない is its copular form used after nouns and na-adjectives to state a required identity or condition.
べき
べき expresses that something should or ought to be done based on judgment or duty, whereas でなければならない more directly states that a certain identity or condition is required.

Written forms

でなければいけない
Everyday variant with いけない; often feels a little more conversational than でなければならない.
でなければならぬ
Stiff, literary, or old-fashioned variant using ならぬ instead of ならない.

Etymology

Formed from copular で plus なければ, the conditional of ない, plus ならない, literally 'if it is not ..., it will not do.' The variant ならぬ uses an older or more literary negative form of なる.