This document discusses modal verbs related to obligation and prohibition. It explains that "have to" expresses obligation from an external source like rules or another person, while "must" expresses self-imposed obligation. "Mustn't" and "don't have to" are used for prohibition and absence of obligation respectively. Examples are provided to illustrate the proper usage of each modal verb in expressing obligation, prohibition, or lack of necessity.

1. MODAL VERBS (I):MODAL VERBS (I):
Must, have to, don’t have to,Must, have to, don’t have to,
mustn’tmustn’t

2. OBLIGATIONOBLIGATION
Have toHave to
(+) She has to get up at 7 every day.(+) She has to get up at 7 every day.
You have to drive on the left in the UK.You have to drive on the left in the UK.
(?) Do we have to study this for the exam?(?) Do we have to study this for the exam?
Does he have to tidy his room?Does he have to tidy his room?

3.  UseUse have tohave to to talk aboutto talk about rulesrules andand
obligationsobligations, or to say that, or to say that
something is necessary.something is necessary.
I have to study harder if I want toI have to study harder if I want to
pass the exam.pass the exam.
Muslims have to pray 5 times a day.Muslims have to pray 5 times a day.

4. Must, mustn’tMust, mustn’t
(+)You must do your homework tonight.(+)You must do your homework tonight.
She must wash the dishes before sheShe must wash the dishes before she
leaves.leaves.
(-) You mustn’t smoke in class.(-) You mustn’t smoke in class.
They mustn’t leave their bags here.They mustn’t leave their bags here.
(?) Must I do the homework?(?) Must I do the homework?
(mustn’t = must not)(mustn’t = must not)

5.  UseUse must + infinitivemust + infinitive to talk aboutto talk about
rules and obligations.rules and obligations.
 MustMust is a modal verb. The onlyis a modal verb. The only
forms areforms are mustmust andand mustn’t.mustn’t.
 MustMust, as, as ALL MODALSALL MODALS, is ALWAYS, is ALWAYS
followed by infinitivefollowed by infinitive WITHOUTWITHOUT
TO!!!TO!!!

6. Must vs. Have toMust vs. Have to
 Both indicate obligation, but there’s a littleBoth indicate obligation, but there’s a little
difference.difference.
It’s getting late. IIt’s getting late. I mustmust go nowgo now 
obligation from theobligation from the speakerspeaker..
It’s getting late. My mum told me IIt’s getting late. My mum told me I havehave
toto be at home at 9.be at home at 9.  obligation fromobligation from
another personanother person..

7. OBLIGATIONOBLIGATION
FROM THE SPEAKERFROM THE SPEAKER FROM ANOTHERFROM ANOTHER
PERSONPERSON
II mustmust go to bed. I’mgo to bed. I’m
exhausted.exhausted.
II mustmust remember toremember to
phone her tomorrowphone her tomorrow
– it’s her birthday.– it’s her birthday.
YouYou have tohave to wear awear a
seatbelt in the car.seatbelt in the car.
Do youDo you have tohave to workwork
on Saturdays?on Saturdays?
II had tohad to wear awear a
uniform when I wasuniform when I was
at school.at school.

8. PROHIBITION:PROHIBITION:
mustn’tmustn’t
 Don’t have toDon’t have to andand mustn’tmustn’t are completelyare completely
different. Comparedifferent. Compare
YouYou mustn’tmustn’t smoke inside a hospital. It’ssmoke inside a hospital. It’s
forbidden.forbidden. ((It’s the lawIt’s the law))
YouYou mustn’tmustn’t drink and drive.drink and drive.
YouYou don’t have todon’t have to drive to the party, I’lldrive to the party, I’ll
pick you up.pick you up. (You can drive if you want,(You can drive if you want,
butbut it is not necessaryit is not necessary).).

9. NO OBLIGATION/NECESSITY:NO OBLIGATION/NECESSITY:
YouYou don’t have todon’t have to come to the partycome to the party
if you don’t want to.if you don’t want to.
YouYou don’t have todon’t have to pay for thepay for the
photocopies, they are free.photocopies, they are free.
Don’t have to

10. Complete the sentences with: have to, must,Complete the sentences with: have to, must,
don’t have to, mustn’tdon’t have to, mustn’t
It is forbidden. You ______ do that.
You ______ ask my permission. You can do what
you want.
You ______ speak to the driver when the bus is
moving. It's dangerous.
mustn’t
mustn’t
don’t have to
In athletics, you ______ start when the gun is fired.
have to
I _________ do my homework tonight.
must

11. The train is direct. You ______ change trains.
I like Saturdays because I ______ go to work.
In bridge, you ______ look at other people's cards.
Whatever you do, you ______ click with the right
mouse button or the program will crash.
don’t have to
mustn’t
don’t have to
mustn’t
I ______ wear a suit at work. My boss is very formal.
have to