Unit 20: Modals 2: obligation, probability, possibility
Ngữ pháp Modals 2: obligation, probability, possibility
📘 Giải thích tiếng Việt
Obligation – Sự bắt buộc
Nghĩa vụ ở hiện tại/tương lai dùng must, have to, need to: All visitors must turn off their phones. Trong văn nói, have to phổ biến hơn; must hay dùng trong thông báo, quy định viết.
Không bắt buộc (không cần thiết) dùng don't have to / don't need to / needn't. Quá khứ dùng had to (bắt buộc) và didn't have to / didn't need to (không cần).
Phân biệt mustn't và don't have to
Hai cấu trúc này KHÁC nghĩa. mustn't = cấm, không được phép (You mustn't do that!). don't have to = không cần thiết, làm hay không tuỳ bạn (You don't have to do that.).
Probability – Xác suất cao
Khi khá chắc chắn nhờ có bằng chứng, dùng must (chắc là đúng) và can't / couldn't (chắc là không): The phone's ringing – it must be Simon. / It can't be from Japan.
Probability & possibility – Khả năng vừa phải
Điều có thể xảy ra/đúng dùng should hoặc ought to (We should hear from Cheryl this weekend.). Điều có thể (không chắc) dùng could / may / might: It could / may / might be Polish.
Tổng điểm: 0/38
Theory
Obligation
| Use | Modal | Example |
|---|---|---|
| Present or future obligation | must / mustn't have to need to | All visitors must turn off their mobile phones. You have to / need to press 'send'. |
| No present or future obligation | don't have to don't need to needn't | You don't have to / don't need to / needn't pay to send an e-mail. |
| Past obligation | had to | Yesterday, Sam had to buy more stamps. |
| No past obligation | didn't have to didn't need to | I learnt a little Italian, but everyone spoke English, so I didn't have to / didn't need to use it. |
Helpful hints
In spoken English, have to is more common than must. Must is often used in written notices and instructions.
✓ 'We have to pay the phone bill today,' Rita said.
✓ Passengers must turn off all mobile phones.
In spoken English, have to is more common than must. Must is often used in written notices and instructions.
✓ 'We have to pay the phone bill today,' Rita said.
✓ Passengers must turn off all mobile phones.
Watch out! Mustn't and don't have to do not mean the same.
✓ You mustn't do that! (= Don't do that!)
✓ You don't have to do that. (= You can do that if you want to, but it's not necessary.)
✓ You mustn't do that! (= Don't do that!)
✓ You don't have to do that. (= You can do that if you want to, but it's not necessary.)
Probability and possibility
| Use | Modal | Example |
|---|---|---|
| Present strong probability | must can't couldn't | The phone is ringing – it must be Simon. This letter can't / couldn't be from Japan because it's got a French stamp. |
| Present and future probability | should ought to | We ought to / should hear from Cheryl this weekend. |
| Present and future possibility | could may might | I'm not sure what language it is – it could / may / might be Polish. |
Helpful hints
We often use must, can't and couldn't for probability when we have some evidence for our opinion.
✓ I just rang Paul, but there's no answer. He must be out.
We often use must, can't and couldn't for probability when we have some evidence for our opinion.
✓ I just rang Paul, but there's no answer. He must be out.
Watch out! To talk about possibility and probability about the past, we use a modal and the perfect infinitive. See Unit 22.
Exercise A
A Score: 0/8
Choose the sentence (A, B or C) which means the same as the first sentence.
1
We have to pay the electricity bill before Friday.
A We can pay it if we want to.
B We must pay it.
C We've already paid it.
A We can pay it if we want to.
B We must pay it.
C We've already paid it.
B – We must pay it.
2
You don't need to buy me a birthday present.
A You must buy me a birthday present.
B It's not necessary to buy me a birthday present.
C You mustn't buy me a birthday present.
A You must buy me a birthday present.
B It's not necessary to buy me a birthday present.
C You mustn't buy me a birthday present.
B – It's not necessary to buy me a birthday present.
3
I have to do some work on my project this evening.
A I haven't got time to do the work.
B I've already done the work.
C I need to do the work.
A I haven't got time to do the work.
B I've already done the work.
C I need to do the work.
C – I need to do the work.
4
Lenny didn't have to see the head teacher after all.
A It wasn't necessary for Lenny to see the head teacher.
B Lenny went to see the head teacher.
C Lenny is waiting to see the head teacher.
A It wasn't necessary for Lenny to see the head teacher.
B Lenny went to see the head teacher.
C Lenny is waiting to see the head teacher.
A – It wasn't necessary for Lenny to see the head teacher.
5
Students mustn't run in school buildings.
A They can run if they want to.
B Students don't like running.
C Running isn't allowed.
A They can run if they want to.
B Students don't like running.
C Running isn't allowed.
C – Running isn't allowed.
6
All passengers must fasten their seatbelts.
A They have to fasten their seatbelts now.
B They don't have to fasten their seatbelts.
C They can fasten their seatbelts.
A They have to fasten their seatbelts now.
B They don't have to fasten their seatbelts.
C They can fasten their seatbelts.
A – They have to fasten their seatbelts now.
7
Mr Reed had to go to the police station to answer some questions.
A Mr Reed was able to go to the police station.
B Mr Reed forgot to go to the police station.
C Mr Reed was obliged to go to the police station.
A Mr Reed was able to go to the police station.
B Mr Reed forgot to go to the police station.
C Mr Reed was obliged to go to the police station.
C – Mr Reed was obliged to go to the police station.
8
It's kind of you to offer to help, but you really don't need to.
A I don't want you to help me.
B Your help isn't necessary.
C You won't be able to help me.
A I don't want you to help me.
B Your help isn't necessary.
C You won't be able to help me.
B – Your help isn't necessary.
Exercise B
B Score: 0/8
Circle the correct word or phrase.
1
'Smoking isn't allowed in the airport.'
You mustn't / don't have to smoke in the airport.
You mustn't / don't have to smoke in the airport.
mustn't
2
'It's not necessary to come to the train station to meet me.'
You have to / don't have to meet her at the train station.
You have to / don't have to meet her at the train station.
don't have to
3
'We were forced to wait for over two hours in the rain!'
They had to / didn't need to wait for over two hours in the rain.
They had to / didn't need to wait for over two hours in the rain.
had to
4
'The instructions tell you to write in pencil.'
You must / needn't write in pencil.
You must / needn't write in pencil.
must
5
'You can contact us by either phone or e-mail.'
You mustn't / don't have to phone them.
You mustn't / don't have to phone them.
don't have to
6
'In my country, you can carry your passport with you if you want, but it's not necessary.'
In her country, you don't need to / mustn't carry your passport with you.
In her country, you don't need to / mustn't carry your passport with you.
don't need to
7
'My grandfather was made to start work when he was just fourteen years old.'
He had to / must start work when he was just fourteen years old.
He had to / must start work when he was just fourteen years old.
had to
8
'It's not necessary to book a hotel; you can stay in our spare room.'
You mustn't / don't have to stay in a hotel.
You mustn't / don't have to stay in a hotel.
don't have to
Exercise C
C Score: 0/6
Complete using the correct form of have to. You may have to use some negative forms.
1
Jade can't come out tonight. She __________ look after her little brother.
has to
2
I didn't have enough money, so I __________ borrow some from Yuri.
had to
3
It's raining really hard, but luckily we __________ go out this evening.
don't have to
4
To start the laptop you __________ press the power button.
have to
5
Robbie worked last weekend, but I __________.
didn't have to
6
__________ you __________ go to piano lessons when you were younger?
Did … have to
Exercise D
D Score: 0/8
Match the sentences with the explanations. You may have to use some of the explanations more than once.
A I'm almost certain.
B It's probable.
C Maybe / Perhaps.
B It's probable.
C Maybe / Perhaps.
1
'Someone is at the door. It must be Mrs Johnson from next door.'
A – I'm almost certain.
2
'Lena might not know where the cinema is.'
C – Maybe / Perhaps.
3
'Dad should know what the capital of New Zealand is.'
B – It's probable.
4
'Greg can't be in the final! He's a terrible player!'
A – I'm almost certain.
5
'The dog is wet. It must be raining outside.'
A – I'm almost certain.
6
'We may go to the Canary Islands for Easter.'
C – Maybe / Perhaps.
7
'Ken must like that film. He's seen it six times!'
A – I'm almost certain.
8
'Barry ought to be able to cook Chinese food. He lived there for two years.'
B – It's probable.
Exercise E
E Score: 0/8
Rewrite the sentences using the words given.
1
You're expecting David to ring. The phone rings. must
That/It must be David.
2
Anna is a better runner than Rula. You think Anna will probably win the race tomorrow. should
Anna should win the race tomorrow.
3
A letter arrives. It's possible that it's from your cousin, Janice. could
It/The letter could be from Janice.
4
There's a knock at the door. Your mum says it might be Colin, but you know Colin is on holiday. can't
It can't be Colin.
5
You see someone wearing a costume. You think there's a strong probability that she's going to a fancy-dress party. must
She must be going to a fancy-dress party.
6
Your sister is looking for her hairbrush. You think it's possible that it's in the living room. might
It might be in the living room.
7
You're waiting for Harriet to arrive. You think she'll probably be there in half an hour. should
She/Harriet should be here/there in half an hour.
8
You're talking about why James seems to be sad. You think it's possible he's in trouble at school. could
He/James could be in trouble at school.
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