Student or Learner
You must / have to wash your hands before you examine each and every patient.
This is from a grammar exercise, you have to circle the correct modal verb. Aren't both of them possible?
For me, 'must' suggests that the speaker/writer is imposing the obligation. 'have to' that the speaker/writer is reporting an obligation imposed by others. This could possibly explain why 'must' can appear to carry more force in writing.
It's not a good question as both could be used- it depends on who is imposing the obligation.