must not for 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 basic structure for must not is:
|subject||+||must not||+||main verb|
The main verb is the base verb.
Look at these examples:
must + not
NB: like all auxiliary verbs, must CANNOT be followed by to. So, we say:
- You mustn't arrive late.
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 can 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 to talk about the past. We use other structures to talk about the past, for example:
- We were not allowed to enter.
- I couldn't park outside the shop.