In general the difference between Must and Have to is connected to personal opinion. If it is your personal opinion to do something then usually we use MUST + BARE INFINITIVE, and if it isn’t connected to your opinion, for example an external situation, then we usually use HAVE TO + BARE INFINITIVE.
- My hair looks like a bird’s nest I must go to the hairdressers.
- I must phone my mother because I’ve not spoken to her for a month.
- My nephew has to go to school
- I had to walk home last night as I missed the last bus.
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