Obligation and Necessity
Must and Mustn’t
- You use MUST to give people orders or to
make strong suggestions. This is especially common when you are in a
position of authority. EG a parent talking to a child.
- You must be home by ten! (You can’t stay
out later than ten.)
- You must listen to me. (You can’t not
listen to me.)
- You use MUSTN’T to give a negative order
to someone or to tell them about a negative order.
- You mustn’t talk to strangers. (You
can’t talk to strangers. It might be dangerous.)
- You mustn’t park here. (You can’t park
here. There’s a ‘No Parking’ sign.)
- You use MUST and MUSTN’T to talk about an
obligation you feel.
- I must post this letter.
- We mustn’t be late for the lecture.
Have to, Don’t have to and Needn’t
- You use HAVE TO to talk about obligations
that come from other people. Often the ‘other people’ are the police, the
government, the law, teachers etc. In the positive form, HAVE TO is very
similar to MUST.
- You have to drive on the left. (You
can’t drive on the right. Te law says you must drive on the right.)
- You use DON’T HAVE TO and NEEDN’T to say
something is unnecessary.
- I don’t have to get up early tomorrow.
(It isn’t necessary)
- You needn’t get up early tomorrow.
- DON’T HAVE TO & NEEDN’T are very
different in meaning to MUSTN’T.
- You mustn’t leave. (You can’t leave. You
have no choice)
- You don’t have to leave. (You can stay
or go, it’s your choice)
Form of Must, Have to and Needn’t
- Be careful! MUST doesn’t have a past or
future form. You use HAD TO to talk about the past and WILL HAVE TO to
talk about the future.
- He had to start work at six. (not “
- You’ll have to find a job. (not “
- You use the infinitive without to after
MUST and NEEDN’T
- You must call me
- You mustn’t smoke
- You needn’t worry