Must, have to, should, ought to

1. must, have to, should, ought to
EF intermediate 4B

2. OBLIGATION
HAVE TO/MUST (+ INFINITIVE)
Have to and must are normally
used to talk about obligation
or something which is
necessary to do

3. Have to (+ inf)
Have to is NOT an auxiliary, but a
normal verb.
It exists in all tenses and forms
(also gerund and infinitive)
You need the axiliary DO for
questions (and negatives*).

4. You have to wear a seatbelt in a car
Do you have to work on Saturdays?
I’ll have to get up early tomorrow. My
interview is at 9.0
I had to wear a uniform at my primary school
Do you like having to come to class every day?

5. Must (+ inf)
Must is a modal verb.
It only exists in the present (it can
be used with a future meaning)
For OBLIGATION in other tenses
use have to.

6. You must remember to phone Emily – it’s her
birthday
You must be on time tomorrow because
there’s a test
When I was a child my father told me I had to
work hard to achieve my goals*

7. Must or have to?
They have a very similar meaning. You can
usually use either.
Have to is more common for general, external
obligations (rules and laws)
Must is more common for specific or personal
obligations
Both can be used for strong recommendations

8. I have to wear a shirt and tie at work
(= it’s the rule of the company)
I must buy a new shirt – this one is too
old
(= it’s my own decision)
You have to/must see this film. It’s
great!

9. Have got to is also common instead of
have to/must in spoken English
I’ve got to go now. It’s very late

10. NO OBLIGATION
DON’T HAVE TO (+ INFINITIVE)
Use don’t have to when there is
NO obligation/it’s not
necessary to do something

11. You don’t have to pay – this museum is
free
You don’t have to go to the party if you
don’t want to.
You don’t have to drive – we can get a
train

12. PROHIBITION
MUSTN’T (+ INFINITIVE)
Use mustn’t when something is
prohibited
You can often use can’t or not
allowed to instead of mustn’t
with the same meaning

13. You mustn’t feed the animals.
You mustn’t overtake on the left lane.
You mustn’t smoke in the classroom.
You mustn’t/can’t/aren’t allowed to feed the
animals.
You mustn’t/can’t/aren’t allowed to overtake on the
left lane.
You mustn’t/can’t/aren’t allowed to smoke in the
classroom.

14. ADVICE, OPINION
SHOULD/SHOULDN’T (+ INFINITIVE)
Should/shouldn’t is not as strong as
must/have to.
It’s a modal verb and it only has those two
forms.
You can use ought (not) to instead of
should/shouldn’t with the same meaning

15. You should take warm clothes with you
to Dublin. It might be cold at night.
You shouldn’t drink so much coffe. It
isn’t good for you.
I think the government should do
something about unemployment.

16. You ought to take warm clothes with
you to Dublin. It might be cold at night.
You ought not to drink so much coffe.
It isn’t good for you.
I think the government ought to do
something about unemployment.

17. OBLIGATION
EXTERNAL HAVE TO
(HAVE GOT TO)
SPECIFIC
PERSONAL MUST
(HAVE GOT TO)
STRONG
RECOMMENDATION
HAVE TO/MUST
(HAVE GOT TO)
NO OBLIGATION DON’T HAVE TO
PROHIBITION MUSTN’T
ADVICE,
OPINION
SHOULD
OUGHT TO