Learn English > Grammar > Verbs > Modals > have to, must have to, must Have to is NOT an auxiliary verb (it uses the verb have as a main verb). We include have to here for convenience. Must is a modal auxiliary verb. In this lesson we look at have to, must and must not, followed by a quiz to check your understanding. have to for objective obligation We often use have to to say that something ...

We use have to / must / should + infinitive to talk about obligation, things that are necessary to do, or to give advice about things that are a good idea to do.

MUST is a modal verb. With modals verbs, there is only one form of it for every subject pronoun: I must You must He must She must It must We must They must You see there is no change in the word MUST. Just like the other modal verbs, there is never an S at the end of must: He musts stop. (This is NOT CORRECT) He must stop. (This is CORRECT) After Must we have the verb, or more specifically ...

"Must" is a modal verb most commonly used to express certainty. It can also be used to express necessity or strong recommendation, although native speakers prefer the more flexible form "have to."