Modal verbs — can, should, must
Modal verbs — little helpers
- Modal verbs add meaning: ability, advice, obligation.
- can, could, should, must, have to.
- They are followed by the base verb (no to, no -s).
can / could — ability & requests
- can = ability or possibility: I can swim.
- could = past ability, or a polite request: She could read at four. Could you help me?
- After can / could, use the base verb: can swim (not can to swim).
Which sentence is correct?
A modal is followed by the base verb (no “to”, no -ing): “can swim”.
should — advice
- should = advice, "it's a good idea": You should see a doctor.
- Negative shouldn't = "it's not a good idea": You shouldn't eat so late.
- It is softer and gentler than must.
Give advice: You ___ see a doctor. (use one modal verb)
Advice → should: “You should see a doctor.”
Translate into English: 你应该去看医生。
Advice → should + base verb: “You should see a doctor.”
must / have to — obligation
- must and have to = "it's necessary": You must wear a seatbelt. I have to get up early.
- mustn't = it's forbidden: You mustn't smoke here.
- don't have to = it's not necessary: You don't have to come.
What does the modal do?
can = ability; should = advice; must / have to = obligation.
“You mustn't smoke here.” — Does this mean it is forbidden?
mustn't = it is forbidden. (don't have to = not necessary — different!)
Common mistakes
- ❌ You must to go. → ✓ You must go. — modals never take to.
- ❌ She musts study. → ✓ She must study. — modals never take -s.
- Careful: mustn't = not allowed; don't have to = not necessary. Opposite meanings!
Match each sentence to its meaning.
mustn't forbids; don't have to means it's optional; should advises; must requires.
Complete with the past of “must”: Yesterday I ___ work late.
must has no past form — use had to.
- Modals + base verb (no to, no -s).
- can / could = ability & requests; should = advice.
- must / have to = necessary; mustn't = forbidden ≠ don't have to = not necessary.
A friend is tired and stressed. Write one sentence of advice using “should”.
Example: “You should go to bed early and relax.”