Grammar › Must, have to and should
Mustn't, don't have to and shouldn't
450 fill-in-the-gap exercises, 45 tests of ten
Mustn't forbids. Don't have to says there is no need. They are not the same.
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Getting your first question ready.
The difference, stated plainly
- mustn’t = there is a rule against it. You mustn’t park on the crossing.
- don’t have to = there is no rule either way. You don’t have to wear a tie.
A quick test: if you could add if you like, the sentence needs don’t have to.
shouldn’t in the middle
Shouldn’t is advice against something, not a prohibition:
You shouldn’t drive when you’re this tired.
Nobody is forbidding it; you are being told it is a bad idea.
The past
Mustn’t has no past. For something that was forbidden, English uses wasn’t allowed to or couldn’t:
We weren’t allowed to leave the building.
Didn’t have to is the past of don’t have to:
We didn’t have to pay — it was included.
needn’t
Needn’t means the same as don’t have to and is more common in British English:
You needn’t wait.
Note the difference in the past: needn’t have done means you did it and it was unnecessary, while didn’t need to do usually means you did not do it at all.
All forms
| Form | Meaning | Example |
|---|---|---|
| mustn't | forbidden | You mustn't smoke in here. |
| don't have to | not necessary | You don't have to come. |
| doesn't have to | not necessary | She doesn't have to come. |
| shouldn't | unwise | You shouldn't eat so late. |
| didn't have to | was not necessary | We didn't have to pay. |
Examples
Taken from the 450 sentences in this drill. The answer is highlighted.
- You don't have to wear a jacket. It's hot outside.
- I shouldn't forget to buy milk, it's an important item on the shopping list.
- We mustn't eat this cake, it's for a special occasion.
- He doesn't have to submit his work by tomorrow, there's no deadline.
- I don't have to call my mom later, it's not urgent.
- The doctor said Susan shouldn't eat sugary foods because of her condition.
- He mustn't talk during the movie or he will disturb others.
- He doesn't have to check his email constantly, once a day is enough.
- You don't have to watch that movie. It's not worth your time.
- You shouldn't forget to water the plants when you go on vacation.
- Children mustn't play near the lock gates; the sign forbids it.
- She doesn't have to tell you if she doesn't want to.
Mistakes to avoid
Wrong: You mustn't bring food, but you can if you want. correct: You don't have to bring food, but you can if you want.
Mustn't forbids, which contradicts the rest of the sentence.
Wrong: She doesn't must work on Sundays. correct: She doesn't have to work on Sundays.
Must never takes do. The negative of an obligation that has gone away is don't have to.