What are modal verbs?
Modal verbs (can, could, may, might, must, should, will, would) are helper verbs that add meaning such as ability, permission, advice or possibility. They are always followed by the base verb (without to), and they never take -s.
Subject
She
Modal
can
Base verb
swim
| Modal | Meaning | Example |
|---|---|---|
| can | ability, permission, possibility | I can swim. Can I sit here? |
| could | past ability, polite request | I could read at four. Could you help me? |
| should | advice, a good idea | You should see a doctor. |
| must | strong obligation, strong certainty | You must wear a seat belt. He must be tired. |
| have to | obligation (a rule or situation) | I have to work on Saturday. |
| might / may | possibility (not sure) | It might rain. She may be at home. |
| mustn’t | it is forbidden | You mustn’t smoke here. |
| don’t have to | it is not necessary | You don’t have to come. |
Rule
Form
- Modal + base verb: She can speak French. (not “can speaks” or “can to speak”).
- Negative: add not / n’t: can’t, couldn’t, shouldn’t, mustn’t, might not.
- Question: put the modal first: *Can you swim? *Should I go?
- No -s, no -ing, no past form (except could, might): use was able to / had to in other tenses.
might
possible
should
advice
must
very strong
Lots of examples
- She can speak three languages.Ability.
- Can I use your phone?Permission.
- Could you open the window, please?Polite request.
- When I was five, I could swim.Past ability.
- You should drink more water.Advice.
- You shouldn’t stay up so late.Negative advice.
- You must show your ticket.Obligation.
- Children mustn’t play on the road.Prohibition.
- I have to get up at six on weekdays.Obligation.
- We don’t have to wear a uniform.Not necessary.
- It might snow tomorrow.Possibility.
- He must be at work. His car is outside.Strong certainty.
Don’t say / Say
Don’t sayShe cans swim.
SayShe can swim.Why: No -s on modals.
Don’t sayI must to go.
SayI must go.Why: No to after a modal.
Don’t sayHe should goes.
SayHe should go.Why: Base verb.
Don’t sayYou don’t must smoke.
SayYou mustn’t smoke.Why: Modals form negatives with not.
Don’t sayDo you can swim?
SayCan you swim?Why: No do with modals.