Must not, Mustn’t, the prohibition
We express a prohibition
Must is an auxiliary verb.
It is followed by a main verb.
The structure for must not is:
subject + must not + infinitive without « to ».
Must not (or mustn’t): negative form of must.
We use must not to say that something is not permitted or allowed.
Example: Passengers must not talk to the driver.
Must not is often contracted to mustn’t.
I mustn’t forget my keys.
You mustn’t disturb him.
Students mustn’t be late.
Use: 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).
Examples:
I mustn’t eat so much chocolate. (subjective)
You mustn’t play so much videogames. (subjective)
Students must not leave bicycles here. (objective)
Policemen must not drink on duty. (objective)
Tenses: must not to talk about the present or the future:
Visitors must not smoke. (present)
I mustn’t forget Tara’s birthday. (future)
For the past, we don’t use must not/mustn’t: We use other structures.
We were not allowed to go inside.
I couldn’t park in front of the shop.