Obligation (verplichting/moeten)
have to = external obligation / must = internal
- Have (got) to -> an obligation from OUTSIDE the speaker (someone else made the rules); all tenses
We have(got) to wear a uniform at the reception desk. / Miss, when do we have (go) to hand in our homework?
Al couldn't join us last night, unfortunately he had (got) to work.
As a tour operator, she has always had to deal with difficult customers.
He had had to cancel the flight due to the pandemic restrictions.
They will now have (got) to find a new flight for new year.
-> an obligation from the speaker him-/herself
We use mustn't particularly when the prohibition comes from the speaker.
(Parent to child) You must apologize to your sister.
(Teacher to student) You mustn't be late to class.
I mustn't let that happen again.