These constructions are not grammatically the same as modal verbs (Unit 27), but they have a modal meaning. We always use the base form of the verb (Unit 14) after them.

Be able to

We use it to talk about ability. It is more polite than can (Unit 28) or could (Unit 29).

Will you be able to check-in before 3:00pm?
I'm afraid I may not be able to check-in until after 6:00pm.
Unfortunately, I wasn't able to confirm our reservation over the phone.

Ought to

We use it for advice, necessity and probability (exactly the same way as should in Unit 33).

You ought not to enter without knocking.
I think we ought to have apologized.
Fresh towels ought to be on the housekeeping cart.

Have got to

We use it to talk about necessity for present or future time (the same as have to in Unit 34).

Have you got to work tomorrow?
I've got to finish cleaning this room before I go home.

Had better

We use it for advice and necessity for a particular present or future time. It is stronger than ought to (above) or should (Unit 33).

I think you'd better ask for a wake-up call.
We'd better be quick or we'll miss check-out time.
You'd better not be late again or I'll be very angry.

NOTICE: We nearly always use the short form of had.

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Exercise 36.1
Exercise 36.2