Mustn't vs Don't Have To — Forbidden or Not Necessary
Practice mustn't and don't have to: not allowed vs not necessary. Two negatives that look alike and mean opposite things.
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You ___ use your phone while you're driving. It's dangerous and illegal.
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mustn't
Something is not allowed → 'mustn't'. 'Don't have to' means it isn't necessary, which is not the meaning here. 'Don't must' doesn't exist.
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You ___ tell anyone about the party — it's a surprise for Mum!
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mustn't
Telling anyone would spoil the surprise, so it's not allowed → 'mustn't'. 'Don't have to' would mean you can tell people if you want.
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Tomorrow is Saturday, so I ___ get up early.
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don't have to
There's no work, so getting up early isn't necessary → 'don't have to'. 'Mustn't' would mean getting up early is forbidden.
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Entry to the museum is free, so you ___ pay.
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don't have to
It's free, so paying isn't necessary → 'don't have to'. 'Mustn't pay' would mean paying is forbidden.
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This is a hospital, so you ___ make any noise in the corridors.
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mustn't
Noise in a hospital is not allowed → 'mustn't'. 'Don't have to' would only mean noise isn't necessary.
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You ___ come to the meeting if you're busy, but you can if you want.
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don't have to
'You can if you want' shows it's your choice → 'don't have to' (= not necessary). 'Mustn't' and 'shouldn't' both say you shouldn't come, which contradicts 'you can'.
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My first week at a hotel
Starting a new job at the Harbour Hotel was exciting, but there were a lot of rules to learn. On my first day, I {1} at seven in the morning for training. All staff {2} a uniform. The hotel gives it to you, so you {3} for one yourself. We {4} our phones at reception — they stay in the staff room until our break. Guests {5} the gym and the pool for free whenever they like, but staff can only use them after work. My manager told me I {6} for help whenever I'm not sure about something — she says it's better than guessing. Next month I {7} at night for the first time, which I'm a bit nervous about. Still, if I work hard, I {8} a better job here one day.
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1. had to arrive — 'On my first day' is the past, and 'must' has no past form → 'had to arrive'.
2. have to wear — A rule for everyone at work → 'have to wear'. 'Must to wear' is wrong: 'must' is never followed by 'to'.
3. don't have to pay — The hotel gives you the uniform, so paying isn't necessary → 'don't have to pay'. 'Mustn't pay' would mean paying is forbidden.
4. mustn't use — The phones stay in the staff room, so using them at reception is not allowed → 'mustn't use'.
5. can use — Guests are allowed to use the gym for free → 'can use' (permission).
6. should ask — The manager is giving advice — asking is better than guessing → 'should ask'.
7. will have to work — 'Next month' is the future, and 'must' has no future form → 'will have to work'.
8. might get — A better job is possible, but not certain → 'might get'.
Mustn't or Don't Have To?
Mustn't and don't have to look like a pair, but they mean opposite things. Mustn't says something is not allowed: You mustn't use your phone while driving, You mustn't tell anyone — it's a surprise. Don't have to says something is not necessary: The museum is free, so you don't have to pay, Tomorrow is Saturday, so I don't have to get up early. With don't have to the choice stays with the person — You don't have to come if you're busy, but you can if you want — while mustn't removes it. The confusion is common because the positive forms must and have to are close, and learners expect the negatives to follow. One question settles it every time: can you do it if you want? Yes means don't have to; no means mustn't.
Last updated: · Satori Editorial