Unit 7.1

Must: Modals of Obligation: use

Modal Verbs - 1 minute

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We use must when:

  • We are sure about something, something is reasonably expected (affirmative);
  • There is strong obligation (affirmative, interrogative);
  • Something is necessary (affirmative, interrogative);
  • Prohibition (negative).


Certainty/reasonably expected

  • It must be her dog. The collar says her name.
  • This house must be in a good state! They renovated it last year.
  • Must they be rich? They live in a luxury flat in the city centre.

Strong obligation

  • I must search for a new house, my contract ends soon.
  • She must clean the kids’ clothes, they got very dirty at the park.
  • Must we be on time?


  • I must buy a new bunch of flowers.
  • He must search for a student flat.
  • Must they chop the olive trees down?

Prohibition (negative)

  • You must not give your address on online forums!
  • He must not surf the internet while working!
  • You mustn’t smoke in this restaurant.
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