must do
have to do
Structure
- Verb[な
い] + ければ・ならない
[long form・usually expresses duty or necessity due to widely-accepted moral norms, law, etc.]
[いけない = neutral・ならない = formal/written]
I’m actually going to skip this grammar point because I already knew about it and the lesson doesn’t add any knowledge about differences between it and なければいけない other than the increased formality going into ならない. Maybe would be worth it bringing up how the latter can suggest more having external influences causing the necessity than the former.