Three rules of modal verbs
- A modal is followed by the base form, without to: "You must go" (not must to go, not must goes). The exception is ought to.
- A modal never takes -s: "She can swim" (not she cans).
- Questions and negatives need no do: "Can you help?" · "You shouldn't smoke here."
Have to and need to are not true modals: they change with the subject ("he has to") and use do in questions and negatives ("Do you have to go?").
Common mistakes
- ✗Wrong: He can speaks three languages.✓Right: He can speak three languages.
- ✗Wrong: You must to wear a helmet.✓Right: You must wear a helmet.
Ability
can / could / be able to
can (present) · could (past) · be able to (every tense)
What someone is able to do.
- She can speak four languages.
- When I was young, I could run ten kilometers easily.
- After the course, you will be able to repair this radio.
For one specific success in the past, use was able to or managed to, not could: "The pilot was able to land safely."
Permission and requests
can / could / may
can (informal) · could (polite) · may (formal)
Asking for and giving permission, and making requests.
- Can I use your phone?
- Could you open the window, please?
- May I come in, sir?
- You may leave when you have finished the test.
Would you mind + -ing is a very polite request: "Would you mind closing the door?"
Obligation, no obligation and prohibition
| Modal | Meaning | Example |
|---|---|---|
| must | strong obligation, often from the speaker or a rule | You must wear your ID at all times. |
| have to | obligation from outside: rules, the situation | We have to report at 0600. |
| need to | it is necessary | I need to renew my passport. |
| must not (mustn't) | it is forbidden | You must not smoke near the fuel truck. |
| don't have to, don't need to (British also: needn't) | it is not necessary: you can choose | You don't have to wear a uniform on Sunday. |
| had to | obligation in the past (must has no past form) | We had to walk because the truck broke down. |
ECL tipMust not and don't have to are very different. "You must not tell him" means it is forbidden. "You don't have to tell him" means it isn't necessary.
Advice
should / ought to / had better
should, ought to: advice · had better: strong advice, with a warning
What is a good idea, or the right thing to do.
- You should see a doctor about that cough.
- You ought to check the tires before a long trip.
- You'd better leave now, or you'll miss the bus.
Common mistakes
- ✗Wrong: You had better to hurry.✓Right: You had better hurry.
Possibility and deduction
These modals show how sure you are about something now.
| How sure? | Modal | Example |
|---|---|---|
| almost 100% sure it is true | must | The lights are on. They must be at home. |
| possible | may, might, could | He may be in the office. · It might rain later. |
| almost 100% sure it is not true | can't, couldn't | That can't be John. He's in Germany this week. |
| almost sure it is not true (American) | must not | He must not be home. His car is gone. |
Past modals: modal + have + past participle
| Form | Meaning | Example |
|---|---|---|
| should have + V3 | it was a good idea, but you didn't do it (criticism, regret) | You should have called me. |
| shouldn't have + V3 | you did it, and it was a mistake | I shouldn't have eaten so much. |
| must have + V3 | I am sure it happened | The ground is wet. It must have rained. |
| can't have, couldn't have + V3 | I am sure it didn't happen | He can't have seen us. It was too dark. |
| may have, might have + V3 | perhaps it happened | She might have missed the bus. |
| could have + V3 | it was possible, but it didn't happen; or perhaps it happened | You could have been killed! · He could have missed the bus. |
| didn't need to + verb (British also: needn't have + V3) | it was not necessary (often: you did it anyway) | We didn't need to hurry. The meeting was postponed. |
| would have + V3 | an imaginary past (third conditional) | I would have helped you if I had known. |
Quick check
Choose an answer: the explanation appears straight away.
1You ___ smoke near the fuel depot. It's strictly forbidden.
2His car isn't here. He ___ left already.
3The radio was badly damaged, but the sergeant ___ fix it before the patrol left.
4You ___ buy a new map. I already had one.
5___ I please leave early today, sir? I have a medical appointment.
More practice: sample questions on this topic, with answers.
All 43 questions on this topic, in a new order each time.