Must not, Mustn’t, the prohibition

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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).
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)

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.