Must & Mustn’t (Rules and Prohibition)
Use must for strong obligation and mustn't for prohibition — and learn the key difference between mustn't (forbidden) and don't have to (optional). A2 grammar with 20 questions.
We use must for strong obligation and important rules, and mustn’t for prohibition — things that are not allowed. “You must wear a seatbelt.” “You mustn’t use your phone in the exam.”
How to make it: must + base verb
Like other modals, must never changes and takes the base verb — no -s, no “to.”
| Form | Example |
|---|---|
| Positive | You must be quiet in the library. |
| Negative | You mustn’t (must not) be late. |
The big contrast: mustn’t vs don’t have to
This is the key point of the lesson. These two look similar but mean opposite things.
| Phrase | Meaning |
|---|---|
| mustn’t | It is forbidden — do NOT do it. |
| don’t have to | It is optional — you can choose. |
- You mustn’t smoke here. (it is forbidden)
- You don’t have to smoke. (you can choose not to — it’s optional)
must vs have to
Both express obligation and are often interchangeable. A small guide: must often feels like the speaker’s own strong feeling or a written rule; have to often points to an outside rule. At A2, you can use either for obligation.
- I must finish this today. (I feel it is important)
- I have to wear a uniform. (it’s the school’s rule)
- You must to wear a seatbelt. → You must wear a seatbelt.
- She musts study. → She must study.
- You mustn’t bring a laptop. (when it’s simply optional) → You don’t have to bring a laptop.
Practise must and mustn’t with the 20 questions below — the final lesson of the A2 grammar course!
Check your understanding
Answer the questions below. You will see instantly if you are right.
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