1. A
I
modal verb is an auxilary verb which adds an extra information to the action.
can speak Chinese.Personal
ability
They have to do their homework now.
Obligation
We should train harde
r
to be the champions.
Advice
Do you ride your bike to school?

2. a)
OBLIGATION
Personal duty.
You feel that something is necessary for you to do.
Subject MUST Infinitive Complements
You must wait till the traffic light is green.
He must read the questions twice before answering.
Affirmative:
Interrogative: MUST Subject Infinitive Complements?
Must you wait for your parents at the station?
REMARK
A DUTY HAS NEVER GOT A NEGATIVE FORM

3. b)
OBLIGATION
External obligation. Someone or something obliges you to do something.
Subject HAVE TO Infinitive Complements
You have to tidy your room before going out.
He has to move to London next month.
Affirmative:
Negative: Subject don’t / doesn’t HAVE TO Infinitive Complements
She doesn’t have to fill the car.
We don’t have to wear a uniform at school.
Interrogative: Do / Does Subject HAVE TO Infinitive Complements ?
Do they have to take another maths exam?
Does he have to buy a new computer?

4. PROHIBITION
You are not allowed to do something.
Subject MUSTN’T Infinitive Complements
You mustn’t talk at the library.
We mustn’t smoke on the plane.

5. ADVICE
Someone recommends you to do something.
Subject SHOULD Infinitive Complements
You should be more polite with the clients.
He should study harder.
Affirmative:
Negative: SHOULDN’TSubject Infinitive Complements
shouldn’tHe wait for him. He is always late.
They shouldn’t tell lies.