N4
なければいけない
Must do, Have to do
来月に友達の結婚式に行かなければいけない。
Next month, I have to go to my friend's wedding.
Explanation
「〜なければいけない」 means 'must' or 'have to'; literally, 'if you don't, it won't do'. It is used when the speaker feels a responsibility, or has to do something out of obligation, relationships or self-interest: 「明日までにレポートを出さなければいけない」 (I have to hand in the report by tomorrow). In speech it shortens to 「〜なきゃいけない」 and then just 「〜なきゃ」.
Mixed up with
Versus 「〜なければならない」: 「いけない」 suits personal, immediate matters and sounds conversational; 「ならない」 leans toward social rules, laws and general principles, and appears in official, written and formal settings.
From formal to casual: なければいけません > なければいけない > なきゃいけない > なきゃ.
Easily confused withなければいけない・なければならない: the difference ›