Must and Have to
Must – a strong obligation (in present tenses), also used in formal notices
I must get up early tomorrow.
You must clean your room today.
She must let him go.
People must not leave their bags unattended.
Have to – less strong obligation
I have to leave early tomorrow to catch an earlier bus.
You have to call me about dinner sometime.
He has to ask his wife before he goes.
She has to pick her daughter up from the school.
In past tenses, we use only ‚had to‘ for talking about obligation
I had to leave work early yesterday.
You had to write that email.
He had to call his mum.
She had to talk to him.
We had to meet the deadline.
They had to sell their house in the country.
For future obligations we use will have to
I will have to go to the dentist’s soon.
You’ll have to book a table for Friday.
He’ll have to give the money back.
She’ll have to buy a new dress for the staff party.
We’ll have to take a taxi back home tonight.
They’ll have to change their holiday destination because of a hurricane