Must not (prohibition)
We use must not to say that something is not permitted or
allowed, for example:
- Passengers must not talk to the driver.
Structure of Must not
Must is an auxiliary verb. It is followed by a
main verb. The structure for must not is:
subject + must not + main verb
The main verb is the base verb (infinitive without "to").
Must not is often contracted to mustn't.
Look at these examples:
| subject |
auxiliary must + not |
main verb |
|
| I |
mustn't |
forget |
my keys. |
| You |
mustn't |
disturb |
him. |
| Students |
must not |
be |
late. |
NB: like all auxiliary verbs, must cannot be
followed by to. So, we say:
- You mustn't arrive late. (not You mustn't to
arrive late.)
Use of Must not
Must not expresses prohibition - something that is not
permitted, not allowed. The prohibition can be subjective (the speaker's
opinion) or objective (a real law or rule). Look at these examples:
- I mustn't eat so much sugar. (subjective)
- You mustn't watch so much television. (subjective)
- Students must not leave bicycles here. (objective)
- Policemen must not drink on duty. (objective)
We use must not to talk about the present or the
future:
- Visitors must not smoke. (present)
- I mustn't forget Tara's birthday. (future)
We cannot use must not for the past. We use another
structure to talk about the past, for example:
- We were not allowed to enter.
- I couldn't park outside the shop.
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