Grammar › Modal Verbs › Must & Have to
Must & Have to
'Must' and 'have to' both express obligation, but the source is different:
- Must — obligation from the speaker; strong personal or rule-based need (You must stop).
- Have to — obligation from outside: rules, laws, circumstances (I have to work).
Watch the negatives: 'mustn't' = forbidden; 'don't have to' = not necessary. For the past, use 'had to' (there is no past of 'must').
How to use must and have to
| Meaning | Form | Example |
|---|---|---|
| Obligation from the speaker | must + base verb | You must finish this today. |
| Obligation from outside | have to + base verb | I have to wear a uniform. |
| Prohibition | mustn’t + base verb | You mustn’t touch that. |
| No necessity | don’t have to + base verb | You don’t have to pay. |
| Past obligation | had to + base verb | We had to leave early. |
Must never changes form and takes the base verb. Have to changes like a normal verb: has to, had to, don’t/doesn’t have to.
When to use each
1. Must — the speaker’s obligation
- I must remember to call the dentist. (I feel it)
- You must wear a helmet on site. (a rule the speaker states)
2. Have to — outside obligation
- She has to work on Saturdays. (her job requires it)
- Do I have to book in advance? (asking about the rule)
3. The negatives — very different
- You mustn’t be late. (it’s not allowed)
- You don’t have to be early. (it’s not necessary)
⚠️ Typical error: must has no past. Use had to: I had to wait an hour — not
I must wait an hour yesterday.
Common mistakes
1. Mixing up the negatives. You mustn’t pay, it’s free → You don’t have to pay, it’s free.
2. Using ‘must’ for the past. Yesterday I must work → Yesterday I had to work.
3. Adding ‘to’ after ‘must’. You must to go → You must go. Pro tip: obligation from you = must; obligation from outside = have to; forbidden = mustn’t; not necessary = don’t have to.
✏️ Practice: Must & Have to
1. It's the law: you ___ wear a seatbelt.
2. This is a hospital — you ___ smoke here.
3. Great news — the entry is free, so you ___ pay.
4. My boss says I ___ work this Saturday.
5. Yesterday I ___ leave early to catch a train.
6. She ___ finish the report; it's due at noon.
7. Which sentence means it is NOT necessary?
8. Correct this: 'You must to book a table.'
9. ___ I wear a tie, or is it optional?
10. The children ___ shout in the library. It's a rule.
Frequently asked questions
What is the difference between 'must' and 'have to'?
'Must' usually shows the speaker's own feeling or authority (I must finish this). 'Have to' shows an obligation coming from outside — a rule, law or other people (I have to wear a uniform).
Why are 'mustn't' and 'don't have to' so different?
'Mustn't' means something is forbidden (You mustn't park here). 'Don't have to' means it isn't necessary (You don't have to park here — but you can).
How do I say 'must' in the past?
'Must' has no past form for obligation. Use 'had to': Yesterday I had to work late.
Is 'have got to' the same as 'have to'?
Yes, in speech: I've got to go = I have to go. 'Have got to' is more informal.
👩🏫 For teachers
CEFR objectives for “Must & Have to”:
- Can use 'must' for speaker obligation and 'have to' for external obligation (CEFR B1).
- Can contrast 'mustn't' (prohibition) with 'don't have to' (no necessity).
- Can use 'had to' as the past of obligation.
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