Have to / must + infinitive Have to is more common for genera | English Notes

Have to / must + infinitive

Have to is more common for general, external obligations, for example, rules and laws.
I have to wear a shirt and tie at work. (it's the rule in this company)

Must is more common for specific or personal obligations.
I must buy a new shirt - this one is too old now. (it's my own decision)

We can also use have to or must for strong recommendations.

have to is a normal verb and it exists in all tenses and forms.
must is a model verb. It only exist in the present, but it can be used with a future meaning.

Use don't have to when there is no obligation to do something.
You don't have to pay – the museum is free.

Use mustn't when something is prohibited (not allowing).
You mustn't eat that cake – it's for the party.

We can often use can't or not allowed to instead of mustn't

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