MODAL VERBS (I):
Must, have to, don’t have to,
mustn’t
Have to, don’t have to
(+) She has to get up at 7 every day.
You have to drive on the left in the UK.
(-) We don’t have to wear a uniform.
He doesn’t have to work today.
(?) Do we have to study this for the exam?
Does he have to tidy his room?
 Use
have to to talk about rules and
obligations, or to say that
something is necessary.
I have to study harder if I want to
pass the exam.
Muslims have to pray 5 times a day.
Must, mustn’t
(+)You must do your homework tonight.
She must wash the dishes before she
leaves.
(-) You mustn’t smoke in class.
They mustn’t leave their bags here.
(mustn’t = must not)
 Use
must + infinitive to talk about
rules and obligations.
 Must
is a modal verb. The only
forms are must and mustn’t.
 Must,
as ALL MODALS, is ALWAYS
followed by infinitive WITHOUT
TO!!!
Must vs. Have to

Both indicate obligation, but there’s a little
difference.
It’s getting late. I must go now 
obligation from the speaker.
It’s getting late. My mum told me I have
to be at home at 9.  obligation from
another person.
OBLIGATION
FROM THE SPEAKER
I must go to bed. I’m
exhausted.
I must remember to
phone her tomorrow
– it’s her birthday.
FROM ANOTHER
PERSON
You have to wear a
seatbelt in the car.
Do you have to work
on Saturdays?
I had to wear a
uniform when I was
at school.
No obligation/necessity:
don’t have to.
You don’t have to come to the party
if you don’t want to.
You don’t have to pay for the
photocopies, they are free.
Prohibition: mustn’t

Don’t have to and mustn’t are completely
different. Compare
You mustn’t smoke inside a hospital. It’s
forbbiden. (It’s the law)
You mustn’t drink and drive.
You don’t have to drive to the party, I’ll
pick you up. (You can drive if you want,
but it is not necessary).