segunda-feira, 23 de julho de 2012

Modal verb: Must not/Musn't

Must not, Mustn't (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:

subjectauxiliary must + notmain verb
Imustn'tforgetmy keys.
Studentsmust notbelate.

Note: 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:
  • 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)
  • 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.

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