NOT A TEACHER
Taken from Practical English Usage by Michael Swan:
1 meaning: obligation, certainty
We can use have (got) + infinitive to talk about obligation: things that it is
necessary for us to do. The meaning is quite similar to must; for the
differences, see 361.1.
Sorry, I've got to go now.
Do you often have to travel on business?
Have (got) + infinitive can also be used, like must, to express certainty. (This
used to be mainly an American English structure, but it is now becoming
common in British English.)
I don't believe you. You have (got) to be joking.
Only five o'clock! It's got to be later than that!
2 grammar: with or without do; got
In this structure, have can be used like an ordinary verb (with do in questions
and negatives), or like an auxiliary verb (without do). Got is usually added to
present-tense auxiliary-verb forms.
When do you have to be back? When have you (got) to be back?
Have got to is not normally used to talk about repeated obligation.
I usually have to be at work at eight. (NOT I've usually got to ... )
Progressive forms are possible to talk about temporary continued obligation.
I'm having to work very hard at the moment.
For more details of the use of do-forms and got-forms of have, see 237.
3 future: have (got) to or will have to
To talk about the future, we can use have (got) to if an obligation exists now;
we use will have to for a purely future obligation. Compare:
I've got to get up early tomorrow - we're going to Devon.
One day everybody will have to ask permission to buy a car.
Will have to can be used to tell people what to do. It 'distances' the
instructions, making them sound less direct than must (see 361).
You can borrow my car, but you'll have to bring it back before ten.
For more about 'distancing', see 436.
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