Must and have to (school rules)

[Walt Whitman]

English teacher

Hi everybody.
As far as I know, MUST and HAVE TO are often interchangeable.
When talking about school rules is it better to use MUST or HAVE TO?
For example (teacher speaking):
Students must do their homework. / Students have to do their homework.
Students must be on time. / Students have to be on time.
Students must turn off their mobiles. / Students have to turn off their mobile.

And what about speaking in the first person?
(students speaking)
I must wear a uniform / I have to wear a uniform. Etc.
Thanks a lot.
WW

[5jj]

As far as I know, MUST and HAVE TO are often interchangeable. There is often no significant diference in the affirmative. There is an important difference in the negative.

When talking about school rules is it better to use MUST or HAVE TO? For example (teacher speaking):
Students must do their homework. / Students have to do their homework.
Students must be on time. / Students have to be on time.
Students must turn off their mobiles. / Students have to turn off their mobiles.
'Must' suggests an obligation imposed by the speaker; 'have to' suggests an externally-imposed obligation. If the teacher is imposing the rules, s/he is more likely to use 'must'. If the teacher is explaining what the school rules are, s/he may use 'have to'. There is not really a significant difference.

And what about speaking in the first person?
(students speaking)
I must wear a uniform / I have to wear a uniform. Etc.
The student will normally be talking about an externally-imposed obligation, and so is far more likely to use 'have to'.

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