Have to / Must
Subject + have / has to + present tense verb phrase
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Subject + must + present tense verb phrase
You have to wear a uniform.
I must be at work by 9am.
Have to / must - explain
General rule
Have to = very important, something bad will happen if you do not do it, you have no choice.
Must = something that would be very good if you did it. You have a choice, but you should do it.
You have to wear a uniform.
If you did not wear a uniform, you would lose your job.
I must be at work by 9am.
Being at work by 9am would be be good.
Example 1
A story
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Monday: David arrives at work at 9:05am. Gary is David's boss.
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Gary: David, you must be at work by 9am.
David: Yes, Gary. I will tomorrow.
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Tuesday: David arrives at work at 9:10am.
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Gary: David, remember you must be at work by 9am.
David: Sorry Gary, the trains were late.
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Wednesday: David arrives at work at 9:07am.
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Gary: David, you are late again. You have to be at work by 9am tomorrow. Do you understand?
David: Yes, Gary. Will do. Sorry.
On Monday and Tuesday David was late. Gary said he 'must be' at work by 9am. Sometimes people are late, so it would be good if David made sure he was on time. However, David was late on Wednesday as well. Now, something bad would happen if David was late again. This is why Gary said 'have to'.
Example 2
I have to do my homework.
I will get detention if I don't.
