Grammar · Modal Verbs
Mustn’t vs Don’t Have To
Is it against the rules, or is it just not necessary? Learn the difference with the film Matilda.
Grammar › Modal Verbs › Mustn’t vs Don’t Have To
The rule in one sentenceUse mustn’t when something is against the rules, and don’t have to when something is not necessary — you are free to choose.
About the film
Matilda is a 1996 family film about a very clever little girl who loves books. Her parents think she mustn’t read so much, and they would rather watch TV. At her new school, the head teacher, Miss Trunchbull, is cruel and has many strict rules. In kind Miss Honey’s class, the children don’t have to be afraid.
What does it do?
These two look like a pair, but their meanings are very different. mustn’t means “don’t do it”. There is a rule, and breaking it is wrong or dangerous.
don’t have to means “it isn’t necessary”. Nobody says you must, so you can do it or not. It is your choice, and both answers are fine.
Look at the first and third tiles. They are rules, and there is trouble if you break them. The second and fourth tiles are free choices. Matilda can pay or go if she wants, but she doesn’t need to.
In everyday speech, people almost always use the short forms:
At Miss Trunchbull’s school, you mustn’t make a single mistake. In Miss Honey’s class, you don’t have to hide your ideas.
The first is a strict rule with a punishment. The second gives the children freedom.
Visual guide
Teacher Teddy’s illustrated guide to this rule is being drawn — the full swipe-through infographic will appear here soon.
How to make it
mustn’t — against the rules
Matilda knows she must be quiet in the library.
“Must” is the positive: it is necessary.The children mustn’t eat in the classroom.
No “to” after mustn’t.Are we allowed to use the telephone?
For questions about rules, most people say “allowed to”.don’t have to — not necessary
Matilda has to walk to the library alone.
“Have to” is the positive: it is necessary.She doesn’t have to ask her parents for help.
He, she and it take “doesn’t”.Do we have to read this book tonight?
Use do or does to ask if something is necessary.When to use each one
mustn’t — don’t do it
don’t have to — it’s your choice
Words that help: rule or choice?
Some words near the sentence tell you which one you need.
mustn’t → against the rules
don’t have to → not necessary
Common mistakes
❌ It’s a rule: children don’t have to run in the hall.
✅ It’s a rule: children mustn’t run in the hall.
A rule says “don’t do it”, so use mustn’t.
❌ It’s Saturday, so Matilda mustn’t go to school.
✅ It’s Saturday, so Matilda doesn’t have to go to school.
School isn’t against the rules on Saturday. It just isn’t necessary.
❌ Matilda doesn’t must pay for the books.
✅ Matilda doesn’t have to pay for the books.
“Doesn’t must” is never correct. Use doesn’t have to.
❌ You mustn’t to be late for Miss Trunchbull.
✅ You mustn’t be late for Miss Trunchbull.
No “to” after mustn’t.
One more thing
This part is a little harder. You can come back to it later.
“Mustn’t” has no past form. For a past rule, say wasn’t allowed to or couldn’t. For something that wasn’t necessary in the past, say didn’t have to.
✅ The pupils weren’t allowed to leave early. (a past rule)
✅ She didn’t have to buy her books. The library lent them to her. (not necessary)
Practice: choose the right words
Eight questions. Choose one answer. You get the answer, and why.
1. It’s a school rule. You ___ bring sweets into class.
A rule says “don’t do it” → mustn’t.
2. The library is free. You ___ pay for books.
Paying isn’t necessary → don’t have to.
3. Be careful! You ___ touch the hot oven.
It is dangerous → mustn’t.
4. Matilda ___ go to school on Sunday.
There is no school, so it isn’t necessary → doesn’t have to.
5. Miss Honey says we ___ finish the story today. We can finish it tomorrow.
“We can finish it tomorrow” shows a free choice → don’t have to.
6. Pupils ___ talk when Miss Trunchbull is speaking.
Talking is against her rules → mustn’t.
7. She ___ ask her parents for help with her homework.
“Doesn’t must” is never correct.
8. Last year, the children ___ play outside at lunch. It was a rule.
Mustn’t has no past form → weren’t allowed to.
Your turn
Choose one ending. Then listen to your sentence.
Every sentence here is correct. Pick the one that is true for you. Say it out loud too!
Keep going
This film’s lesson
More lessons
Now hear it in the film
You have just learned mustn’t and don’t have to with Matilda. Now hear the whole film explained in English.
The full listening episode on the same film — a slow, clear movie review with the language used in real speech, and a free transcript.
BeginnerEpisode 73Watch on YouTube