Modal verbs are helping verbs that add meaning to the main verb: how possible, necessary, allowed or advisable something is. The core modals are can, could, may, might, must, shall, should, will, would, plus the "semi-modals" have to, ought to, need to and be able to.
Five grammar rules that apply to every modal
- Modal + base verb (no "to"): I can swim. ✗ I can to swim. (Exceptions: ought to, have to.)
- No -s for he/she/it: She can drive. ✗ She cans drive. ✗ She can drives.
- Negative with "not": cannot / can't, mustn't, shouldn't, won't, wouldn't.
- Questions by inversion — no "do": Can you help? ✗ Do you can help?
- No infinitive or -ing form: you can't say "to can" or "canning" — use be able to instead: I'd like to be able to speak French.
Modal verbs chart by meaning
| Meaning | Modals | Example |
|---|---|---|
| Ability | can, could, be able to | I can type fast. She could read at four. |
| Permission | can, could, may | May I come in? You can sit here. |
| Request | can, could, will, would | Could you send me the file? |
| Possibility | may, might, could | It might rain later. |
| Logical certainty | must, can't | He must be tired. That can't be true. |
| Obligation | must, have to | You must wear a helmet. |
| No obligation | don't have to, needn't | You don't have to come. |
| Prohibition | mustn't, can't | You mustn't smoke here. |
| Advice | should, ought to, had better | You should see a doctor. |
| Offers / suggestions | shall, can, could | Shall I open the window? |
| Future / willingness | will, shall | I'll help you. |
| Past habit | would, used to | We would play outside every evening. |
Ability: can, could, be able to
- can — present ability: She can speak three languages.
- could — general past ability: I could ride a bike when I was five.
- was/were able to — one specific past success: The door was jammed, but we were able to open it. (✗ we could open it sounds odd for a single achievement)
- will be able to — future ability: After this course, you'll be able to write formal emails.
Permission and requests
| Most informal | Neutral / polite | Most formal |
|---|---|---|
| Can I borrow your pen? | Could I borrow your pen? | May I borrow your pen? |
| Can you help me? | Could you / Would you help me? | Would you mind helping me? |
In requests, could and would are not past tense — they are simply softer. They're the safest choice in emails and at work; see polite English phrases.
Possibility and certainty
Modals let you show how sure you are:
| How sure? | Modal | Example |
|---|---|---|
| ~100% (logical conclusion) | must | She's been working all day — she must be tired. |
| Likely / expected | should | The parcel should arrive tomorrow. |
| ~50% | may / might / could | He may be at home. It might snow. That could be the answer. |
| ~0% (logically impossible) | can't / couldn't | That can't be Rahul — he's in London. |
Obligation and necessity: must vs. have to
- must — obligation from the speaker, or written rules: I must call my mother. Passengers must wear seat belts.
- have to — obligation from outside (rules, circumstances): I have to wear a uniform at work. Use have to for other tenses: had to, will have to, have had to.
The big trap: mustn't vs. don't have to
| mustn't = it is not allowed | don't have to = it's not necessary (you can if you want) |
|---|---|
| You mustn't park here. (prohibited) | You don't have to park here — there's space at the back too. (optional) |
| You mustn't tell anyone. (keep it secret!) | You don't have to tell anyone. (it's your choice) |
needn't (British) = don't have to: You needn't bring anything.
Advice: should, ought to, had better
- should — the most common: You should practise speaking every day.
- ought to — same meaning, slightly more formal: You ought to apologise.
- had better ('d better) — strong advice with a warning: You'd better leave now, or you'll miss the train. (Negative: had better not.)
Past modals: should have, could have, must have
| Form | Meaning | Example |
|---|---|---|
| should have done | It was a good idea, but you didn't do it (regret/criticism) | I should have saved my work. |
| shouldn't have done | You did it, but it was a mistake | You shouldn't have shouted. |
| could have done | It was possible, but didn't happen | We could have won the match. |
| would have done | Imaginary past result (third conditional) | I would have helped if you had asked. |
| must have done | Logical certainty about the past | The ground is wet — it must have rained. |
| might / may have done | Possibility about the past | She might have missed the bus. |
| can't / couldn't have done | Past impossibility | He can't have finished already — he only started at ten. |
In speech these contract: should've, could've, would've, must've. Never write "should of" — it's a spelling mistake based on the sound.
Common mistakes
| ✗ Incorrect | ✓ Correct |
|---|---|
| She can sings well. | She can sing well. |
| You must to finish this. | You must finish this. |
| Do you can come tomorrow? | Can you come tomorrow? |
| I will can help you. | I will be able to help you. |
| You mustn't come if you're busy. (meaning optional) | You don't have to come if you're busy. |
| I should of called. | I should have called. |
Practice
Choose the best modal.
- You (mustn't / don't have to) pay — the museum is free.
- (Could / Must) you pass the salt, please?
- Her car isn't outside. She (must / can't) be at home.
- It's very cold. You (should / may) wear a jacket.
- I lost my keys but I (could / was able to) get in through the window.
- You (mustn't / don't have to) use your phone during the exam.
- He's late. He (might have / should have) missed the train.
- I failed the test. I (must have / should have) studied more.
Show answers
- don't have to (not necessary)
- Could (polite request)
- can't (logically impossible)
- should (advice)
- was able to (one specific success)
- mustn't (prohibited)
- might have (past possibility)
- should have (regret)
Modals also appear in conditional sentences (would, could, might), in the passive voice (must be done) and change in reported speech (can → could, will → would).
Frequently asked questions
What are modal verbs?
Modal verbs are helping verbs — can, could, may, might, must, shall, should, will and would — that add meanings such as ability, permission, possibility, obligation or advice to a main verb.
How many modal verbs are there in English?
There are nine core modal verbs: can, could, may, might, must, shall, should, will and would. Ought to, have to, need to and be able to are often taught alongside them as semi-modals.
What is the difference between must and have to?
Both express obligation. “Must” often shows the speaker’s own feeling or a written rule; “have to” shows an outside obligation and is used for past and future forms (had to, will have to).
What is the difference between mustn’t and don’t have to?
“Mustn’t” means something is not allowed (“You mustn’t smoke here”). “Don’t have to” means something is not necessary (“You don’t have to come”).
Can we use “to” after a modal verb?
No. Use the base verb directly after a modal: “I can swim,” not “I can to swim.” The exceptions are the semi-modals ought to and have to.
What does “should have” mean?
“Should have + past participle” means something was the right thing to do but did not happen, so it expresses regret or criticism: “I should have left earlier.”