Modal verbs: "must" and "have to"
"Must" and "have to" are used to express obligation or the "need to do something".
- they can be used interchangeably however.
"MUST": (subjective obligation) in general expresses what the speaker thinks is necessary.
I must stop smoking / We must go it's already midnight /They must work harder.
"HAVE TO": (objective obligation) in general suggests that somebody else has imposed the decision.
In France you have to drive on the right / Tom has to wear a uniform at school.
Tenses:
1- have to can be used in all tenses:
Tom had to wear a uniform last year / Tom will have to wear a uniform next year.
Sonia is having to wait / she may have to come back tomorrow
2- must can be used to talk about the present or the future.
Tom must call his mother tomorrow
but it can't be used to talk about the past ( you use have to)
Interrogative form:
Do you have to leave now? / Must you leave right now?
Negative form:
The negative form of must and the negative form of have to are very different in meaning.
1- must not / mustn't is used to say that something is not allowed
Children mustn't play with fire / Passengers must not talk to the driver / Visitors mustn't smoke.
'must not 'can't be used to talk about the past, you use another structure.
example: we were not allowed to park near the museum
2- don't have to means that there is no obligation to do something, but you can do it if you want.
you don't have to drink alcohol, you can have a soft drink.
she doesn't have to arrive before 9.
"Must" and "have to" are used to express obligation or the "need to do something".
- they can be used interchangeably however.
"MUST": (subjective obligation) in general expresses what the speaker thinks is necessary.
I must stop smoking / We must go it's already midnight /They must work harder.
"HAVE TO": (objective obligation) in general suggests that somebody else has imposed the decision.
In France you have to drive on the right / Tom has to wear a uniform at school.
Tenses:
1- have to can be used in all tenses:
Tom had to wear a uniform last year / Tom will have to wear a uniform next year.
Sonia is having to wait / she may have to come back tomorrow
2- must can be used to talk about the present or the future.
Tom must call his mother tomorrow
but it can't be used to talk about the past ( you use have to)
Interrogative form:
Do you have to leave now? / Must you leave right now?
Negative form:
The negative form of must and the negative form of have to are very different in meaning.
1- must not / mustn't is used to say that something is not allowed
Children mustn't play with fire / Passengers must not talk to the driver / Visitors mustn't smoke.
'must not 'can't be used to talk about the past, you use another structure.
example: we were not allowed to park near the museum
2- don't have to means that there is no obligation to do something, but you can do it if you want.
you don't have to drink alcohol, you can have a soft drink.
she doesn't have to arrive before 9.
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