10. MODAL VERBS

https://learnenglish.britishcouncil.org/en/quick-grammar/modals-1

Ability 

•  I can speak English.

• Could you swim when you were four years old?

Permission

Can, could and may are often used to ask for and give permission.

• Can I sit here?
• You could use my car if you like.
• May I come in?

Advice and suggestion

Should, ought to are often used to give advice and make suggestions.

You should have a rest after working so much.
He ought to smoke less. 
She shouldn't get so nervous in presentations. 
I ought not to doubt about this project. 

Obligation

Have to and must are both used to express obligation. There is a slight difference between the way they are used.

Have to shows us that the obligation comes from somebody else. It’s a law or a rule and the speaker can’t change it.

• Do you have to wear a uniform at your school?
• John can’t come because he has to work tomorrow.
• In Britain you have to buy a TV licence every year.

Must shows us that the obligation comes from the speaker. It isn’t a law or a rule. 

• I must call my dad tonight.
• You must hand in your homework on Tuesday or your mark will be zero.
• You must come and visit us the next time you come to London.

No obligation

We use don’t have to to show that there is no obligation. You can do something if you want to but it’s not compulsory.

• You don’t have to wear a tie in our office. You can wear a tie if you want to but it’s OK if you don’t.
• It’ll be nice if you do but you don’t have to come with me if you don’t want to.
• You don’t have to dress up for the party. Wear whatever you feel comfortable in.

Prohibition

Both can’t and mustn’t are used to show that something is prohibited – it is not allowed.

• You can’t park here, sir.
• You can wear jeans but you can’t wear trainers in that bar.
• You mustn’t speak when the teacher is speaking.

Can’t tells us that something is against the rules. Mustn’t is usually used when the obligation comes from the person who is speaking.

Possibility

May, might are used to express that something is possible.

He may come later. (I feel it is possible)
It might rain this afternoon. (I feel it is possible but I have some doubts)

COMPLETE WITH THE CORRECT MODAL VERB

1. It's very cold today. Do you think itsnow later?
2. Youleave your door unlocked when you go out.
3. They fill the car with petrol before they set off.
4. She   fix her computer. A technician will do it for her.
5. Mum says wewatch TV after we've finished our homework.
6. You pick me up at the station. I can get a taxi.
7. Peter ...................... ride a bike when he was five. 
8. ................. I open de window?
9. You ................ be polite with your customers.  
10. …. They ………………. arrive on time but the traffic is awful today.