Unit 13: Modals
Ngữ pháp Modals: ability, permission, advice, criticism, obligation and necessity, degrees of certainty
📘 Giải thích tiếng Việt
Modals: hình thức
Các modal (can, could, may, might, must, should, will, would) và ought to chỉ có một dạng, theo sau bởi nguyên mẫu không to hoặc perfect infinitive (have + V3): Toby should have recovered by now. Còn have to / need to chia theo ngôi và thì.
Ability & Permission
Khả năng: can (hiện tại), could (quá khứ/giả định); hành động đơn lẻ đã làm được trong quá khứ dùng was/were able to. Xin phép: may lịch sự hơn could, could lịch sự hơn can; quá khứ dùng was allowed to (trừ lời nói gián tiếp vẫn dùng could).
Advice & Criticism
should / ought to để khuyên. Khi + perfect infinitive, chúng phê phán hành động quá khứ đã sai: He should have made more effort. (nhưng đã không làm).
Obligation & Necessity
Must thường là bắt buộc do bản thân; have to do bên ngoài. Phân biệt: mustn't = cấm; needn't / don't have to = không cần thiết. Needn't have done = đã làm nhưng không cần; didn't need to do = không cần nên thường đã không làm.
Degrees of certainty
Chắc chắn: must (khẳng định), can't/couldn't (phủ định). Khả năng cao: should/ought to. Khả năng thấp: could/may/might. Về quá khứ thêm perfect infinitive: She must have been in pain.
Theory
Form
- All modals (will, would, shall, should, can, could, may, might, must) and the semi-modal ought to have only one form.
- Modals are followed by the bare infinitive (simple or continuous) or the bare perfect infinitive.
e.g. Toby should be very fit by now. / Toby should have recovered by now. - The semi-modals have to and need to change their form depending on person and tense.
e.g. The doctor said I had/needed to give up red meat.
Modals: ability
| Use | Modal | Example |
|---|---|---|
| Ability now or generally | can | I can run a kilometre in four minutes. |
| Decisions made now about future ability | can | We can meet at the gym tomorrow, if you like. |
| Ability in the past | could | I could do fifty press-ups with one hand when I was younger. |
| Ability in present, future or general hypothetical situations | could | If only I could quit smoking! |
| Ability in past hypothetical situations | could + perfect infinitive | I could have roasted the potatoes, but I decided that boiling them was healthier. |
⚠️ We use be able to for the infinitive and other tenses:
• I'd love to be able to fit into these jeans again! (infinitive)
• I'll be able to leave hospital in a few weeks. (future)
• I've been able to swim since I was five. (present perfect)
Modals: permission
| Use | Modal | Example |
|---|---|---|
| Asking for and giving permission now, for the future or generally | may / could / can | May / Could / Can I see the doctor, please? |
⚠️ May is more polite than could, and could is more polite than can.
• We don't usually use a modal for past permission: I was allowed to wear a knee support during the match. ✓
• However, we do use could in reported speech: The coach said I could wear a knee support. ✓
Modals: advice
| Use | Modal | Example |
|---|---|---|
| Asking for and giving advice now, for the future or generally | should / ought to | You ought to / should cut down on the amount of red meat you eat. |
Modals: criticism
| Use | Modal | Example |
|---|---|---|
| Criticising past behaviour | should / ought to (+ perfect infinitive) | He ought to / should have made more of an effort with his diet. |
Modals: obligation and necessity
| Use | Modal | Example |
|---|---|---|
| Expressing obligation or necessity | must / have to / need to | I must / have to / need to pick up that prescription. |
| Expressing lack of obligation or necessity | needn't / don't have to / don't need to | You needn't / don't have to / don't need to pick up that prescription. |
| Expressing past obligation | had to | I had to take the pills three times a day for two weeks. |
| Expressing lack of past obligation | needn't (+ perfect infinitive) / didn't have to / didn't need to | I needn't have gone / didn't have to go / didn't need to go to the doctor. |
⚠️ Notes:
• Must is often for personal obligation; have to for external obligation.
• We can use will have/need to for future obligation.
• Use have to for questions (not must): Do I have to take this medicine?
• Must cannot be used as an infinitive. Use have to: I'd hate to have to have injections every day.
• Mustn't = Don't do that! / Don't have/need to = It's not necessary (but you can if you want).
• Needn't + perfect infinitive always refers to an action that happened but wasn't necessary.
Modals: degrees of certainty
| Use | Modal | Example |
|---|---|---|
| Certainty (or near certainty) about now or generally | must / can't / couldn't | That must be the nurse at the door. / These can't / couldn't be the pills. |
| Certainty (or near certainty) about the past | must / can't / couldn't (+ perfect infinitive) | She must have been in a lot of pain. / His leg can't / couldn't have been in plaster for two years! |
| Probability about now, the future or generally | should / ought to | You ought to / should feel better in a few days. |
| Probability about the past | should / ought to (+ perfect infinitive) | The bruise ought to / should have disappeared days ago. |
| Possibility about now, the future or generally | could / may / might | That diet could / may / might be dangerous. |
| Possibility about the real past | could / may / might (+ perfect infinitive) | That could / may / might have been the doctor who rang earlier. |
| Possibility about a hypothetical past | could / might (+ perfect infinitive) | You could / might have become quite ill. |
Exercise A
If a word or phrase in bold is correct, put a tick (✓). If it is incorrect, rewrite it correctly on the line.
Exercise B
Circle the correct word or phrase. If both options are correct, circle both.
Exercise C
Write a form of must, have to, need or need to in each gap to complete the sentences. (Some gaps may have more than one correct answer.)
Exercise D
Complete each second sentence using the word given, so that it has a similar meaning to the first sentence. Write between two and five words in each gap.
Dan __________ his lights are on.
Susie __________ Dobber to the vet since her car's not here.
That __________ Simon. He's much taller!
The Winners __________ tonight; we arranged it for next Tuesday.
You __________ exhausted after such a long journey!
Evan __________ on the phone to someone in Australia!
Casey __________ the disco dancing competition – he's got two left feet!
Helen __________ to call us all day. The phone hasn't rung once.
Exercise E
Use the words in the box only once to complete the sentences in Table A. The meaning of the sentences in Table B will help you.
Exercise F
Circle the correct answer.
Exercise G
Write a modal or semi-modal in each gap to replace the phrase in brackets. Add any other words you need.
Exercise H
Choose the correct answer.
Choosing a gym
Choosing to go to a gym regularly (1) __________ change your life for the better. Don't let it be a decision you regret!
Good gyms have a lot to offer. They (2) __________ provide exercise equipment that is just too expensive to buy and their trained staff are (3) __________ to provide quality health and fitness advice. But if you're planning to join a gym, you (4) __________ definitely ask to look round before you become a member.
Before the law changed a few years ago, anyone (5) __________ set up a gym and even today gyms (6) __________ employ trained fitness instructors. Find out what qualifications the staff have. If they're untrained, it's best to go elsewhere.
You (7) __________ be put off by the gym's hard sell. Just because they want you to sign up – they want your money, after all – that doesn't mean you (8) __________ decide there and then. See a few gyms before you make your final decision.
Ask yourself: What kind of equipment and facilities do they have? There's little point joining a gym and then thinking a few months later, 'I (9) __________ have chosen a gym with a pool.' Do you (10) __________ book equipment in advance, or can you just turn up and use it? How busy does the gym get? It (11) __________ be very pleasant turning up to find there's no room in the changing room and there's a huge queue for each piece of equipment. It (12) __________ also be a good idea to talk to people who already go to that gym to find out their opinion.
Exercise I
Write one word in each gap.
When I broke my arm a week ago, I guess it (1) __________ to have hurt. But it didn't! We were doing PE at school, and we were making a pyramid. We (2) __________ to stand on each other's shoulders. I was right at the top. We (3) __________ have been doing it properly because suddenly the pyramid collapsed and we all fell. I landed on my arm.
Mr Jenkins (4) __________ have known immediately that I'd broken my arm because he sent someone to call an ambulance. 'Sit still, and don't move your arm at all until the ambulance comes,' he said. I (5) __________ still remember the feeling – my arm was numb, and looked very strange, but there was no pain at all. I remember thinking: 'It (6) __________ be broken. If it was broken, I'd be in agony.' I suppose not feeling any pain (7) __________ have been because I was in shock.
The plaster (8) __________ come off in about three weeks but it (9) __________ have to stay on longer. It depends on whether the break has healed properly or not. The next three weeks (10) __________ be the best three weeks of my life – no basketball, no playing in the playground, no swimming – but I'm counting my blessings. It (11) __________ have been a lot worse!
