Modal Verbs: Can, Should, Must
Express ability, advice, and obligation.
Can / Could
Use 'can' for ability or permission in the present, and 'could' for the past or polite requests.
- I can swim.
- Could you help me, please?
- She could read at age four.
Should
Use 'should' to give advice or recommendations.
- You should see a doctor.
- We should leave now.
Must / Have to
Use 'must' or 'have to' for strong obligation or necessity.
- You must wear a seatbelt.
- I have to finish this by Friday.
Might / May for possibility
Use 'might' or 'may' to talk about something that is possible but not certain.
- It might rain later.
- She may already know about the surprise.
- He might be at home right now.
More examples in context
Modal verbs appear constantly in polite, everyday English.
- Can I borrow your charger?
- You shouldn't stay up so late.
- We must submit the report before 5 PM.
- Could I ask you a question?
- You don't have to come if you're busy.
- He must be exhausted after that flight.
Common mistakes to avoid
These are frequent modal verb errors, and how to correct them.
- ✗ She can to swim. → ✓ She can swim. (no 'to' after a modal verb)
- ✗ He musts finish it today. → ✓ He must finish it today. (modals never take -s)
- ✗ You should to see a doctor. → ✓ You should see a doctor.
- ✗ I must to go now. → ✓ I must go now.
Quick practice
Choose the modal verb that best fits each sentence, then check your answer.
- You ___ be quiet in the library. (obligation) (answer: must)
- ___ you help me move this table? (request) (answer: Could)
- It's just a guess, but she ___ be right. (possibility) (answer: might)
- We ___ pay for parking here, it's free. (lack of necessity) (answer: don't have to)
- ___ I use your phone for a minute? (permission) (answer: Can)