UNIT 12: Modal Verbs

HAVE TO / DON'T HAVE TO
We use have to + verb to talk about an impersonal obligation. > I have to go now.
We use don’t have to  + verb to talk about something that is not necessary. > You don’t have to come.

MUST / MUSTN'T
We use must to express a personal obligation. > She is really nice, you must meet her.
We use mustn’t to express prohibition. >You must keep it a secret. You mustn’t tell anyone.

SHOULD / SHOULDN'T
We use should or shouldn’t to give advices, or to ask for advices

CAN / CAN'T
We use can/can’t to express ability and possibility in the present.
COULD /COULDN'T
We use could/couldn’t to express ability and possibility in the past.