In which case we should use must/ have to (mustn't/ don't have to)??? 'Must' is usually used when the speaker expresses /herpersonal opinion, as, I must save him from this danger. 'have to' is generally used when there is obligation from outside: She has to be there at 7 tomorrow morning.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.