Modal verbs are special auxiliary (helping) verbs that change the meaning of the main verb. They express ideas like ability, permission, possibility, obligation, and advice. The main modal verbs in English are: can, could, may, might, will, would, shall, should, must, ought to.
Modal verbs are always followed by the base form of the verb (infinitive without "to").
- ✅ She can swim.
- ✅ You should study.
- ❌ She can to swim.
- ❌ You should studied.
CAN — Ability & Permission
1. Ability (present)
Use can to talk about what someone is able to do right now.
- I can speak three languages.
- She can run very fast.
- He cannot (can't) see without glasses.
2. Permission (informal)
Use can to ask for or give permission in informal situations.
- Can I use your phone? (asking permission)
- You can leave early today. (giving permission)
COULD — Past Ability & Polite Requests
1. Past Ability
Could is the past form of can. Use it for past abilities.
- When I was young, I could run very fast.
- She couldn't sleep last night.
2. Polite Requests
Could is more polite than can for requests.
- Could you help me, please?
- Could I have a glass of water?
3. Possibility (present/future)
- It could rain this evening. (possible)
- That could be the answer.
MAY — Formal Permission & Possibility
1. Formal Permission
May is more formal than can for permission.
- May I come in, sir? (formal — classroom, interview)
- You may begin the test now.
2. Possibility (50% chance)
- She may be late today.
- It may snow tomorrow.
MIGHT — Weaker Possibility
Might expresses a lower possibility than may — less certain, more doubtful.
- I might come to the party. (not sure yet)
- He might be at home. (possible but uncertain)
- It might rain, but I don't think it will.
| Modal | Certainty | Example |
|---|---|---|
| will | 100% certain | I will call you tomorrow. |
| may | ~50% likely | She may join us. |
| might | ~30% likely | He might come. |
| could | ~20–40% | It could work. |
SHOULD — Advice & Recommendation
Use should to give advice, make recommendations, or talk about what is the right or expected thing to do.
- You should drink more water. (advice)
- Students should complete their homework. (expectation)
- You shouldn't eat so much junk food. (negative advice)
- Should I call him now? (asking for advice)
Should is softer than must. "Should" suggests it is a good idea. "Must" says it is absolutely necessary.
MUST — Obligation & Certainty
1. Strong Obligation / Necessity
- You must wear a seatbelt. (law / rule)
- I must finish this report by 5 PM. (personal necessity)
- Students must not cheat in exams. (prohibition)
2. Logical Certainty (deduction)
- She knows every word — she must have studied a lot.
- He is shivering — he must be cold.
Quick Reference Table
| Modal | Main Use | Example |
|---|---|---|
| can | Ability / informal permission | I can drive. |
| could | Past ability / polite request | Could you help me? |
| may | Formal permission / 50% possibility | May I enter? |
| might | Lower possibility / uncertainty | I might come. |
| should | Advice / recommendation | You should rest. |
| must | Strong obligation / logical certainty | You must stop. |
| will | Future / certainty / offers | I will call you. |
| would | Polite requests / past habits | Would you like tea? |
Common Mistakes with Modal Verbs
- ❌ She can to swim. ✅ She can swim.
- ❌ He musts go. ✅ He must go. (no -s with modals)
- ❌ You should to rest. ✅ You should rest.
- ❌ Can I may leave? ✅ May I leave? (not two modals)
Summary
- Can → ability now, informal permission.
- Could → past ability, polite requests, possibility.
- May → formal permission, ~50% possibility.
- Might → lower possibility, uncertainty (~30%).
- Should → advice, recommendation, expectation.
- Must → strong obligation, logical certainty.
- Modal verbs are always followed by the base form of the verb — no to, no -s, no -ing.