Modal verbs · Intermediate (B1)
Must, have to, should: obligation and advice
Rules, necessity and advice: must, have to, don’t have to, mustn’t, should, ought to.
The rules
Must — strong obligation, often from the speaker, or written rules: I must call my mum. Passengers must wear seat belts. Have to — obligation from outside (rules, situations): I have to wear a uniform at work. Past of both: had to.
Mustn’t = it’s prohibited: You mustn’t smoke here. Don’t have to = it’s not necessary (but you can): You don’t have to come — it’s optional. This difference is very important.
Should / ought to — advice and opinion: You should see a doctor. You shouldn’t work so late. Past criticism: should have + participle: You should have told me.
| Form | Meaning | Example |
|---|---|---|
| must / have to | necessary | I have to leave at 6. |
| mustn’t | not allowed | You mustn’t park here. |
| don’t have to | not necessary | You don’t have to pay — it’s free. |
| should | good idea | You should rest. |
Examples
- All visitors must sign in at reception.
- I had to wait two hours at the airport.
- You don’t have to bring anything.
- You should have asked for help.
Common mistakes
✗ You mustn’t pay; it’s free.
✓ You don’t have to pay; it’s free.
Not necessary ≠ prohibited.
✗ I must to go.
✓ I must go.
No to after must.
✗ Yesterday I must work late.
✓ Yesterday I had to work late.
Past of must = had to.
Practice
You ___ touch that wire — it’s dangerous!
Quiz
1.It’s optional. You ___ do it.
2.Complete the sentence.
3.“Mustn’t” means “it isn’t necessary”.
4.Does she ___ wear a uniform?