Student or Learner
My brother was driving my father told him : don't turn right you ( must - have to ) turn left.
Do we use must or have to in this case?
And thanks alot
Generally speaking, 'must' implies an obligation imposed by the speaker, 'have to' an obligation imposed by a third party.
You must do your homework - I, the teacher, impose the obligation.
You have to do your homework. - This is a school rule.
In your example, 'have to' is probably more likely, but it is difficult to say without full context. Even with full context, the information I gave in my first line is not a 'rule'. It is more of an observation on the way the expressions appear to be used most commonly.