Obligation with must/have to and the critical negative split: mustn't (forbidden) vs don't have to (not necessary)
I can express obligation, prohibition and absence of necessity without mixing the negatives.
Look at these examples. Can you spot the grammar pattern?
You mustn't use your phone during the exam, but you don't have to hand it in.
You mustn't use your phone during the exam, but you don't have to hand it in.
I had to wait two hours at passport control — next time I'll have to fly earlier.
I had to wait two hours at passport control — next time I'll have to fly earlier.
Pay attention to the highlighted parts. What do they have in common?
Positives overlap; negatives split dramatically:
| Form | Meaning | Example |
|---|---|---|
| must / have to | obligation | I must go. She has to work on Saturdays. |
| mustn't | prohibition | You mustn't smoke here. |
| don't have to | no necessity | You don't have to pay — it's free. |
must has no past or future: use had to / will have to. Questions prefer have to: Do I have to book?
Apply this grammar in A2 course exercises
Practice Exercisesmustn't read as 'need not'
mustn't = prohibition; don't have to = no necessity
to after must
must + bare infinitive
You mustn't use your phone during the exam, but you don't have to hand it in.
You mustn't use your phone during the exam, but you don't have to hand it in.
Both negatives contrasted in one rule.
I had to wait two hours at passport control — next time I'll have to fly earlier.
I had to wait two hours at passport control — next time I'll have to fly earlier.
Past and future of must via have to.
Practice in course
Apply this grammar in A2 course exercises