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1. Modal verbs

1.2. Advice, necessity, prohibition and obligation

must, have to, need, should, ought to

  • We use must (or have to, which is not a modal verb) to talk about obligation.
  • Applicants must answer the questions honestly.
  • I must finish this essay by Monday.
  • We use mustn't to talk about prohibition.
  • You mustn't eat too many sweets.
  • They mustn't try too hard.
  • We use needn't (or don't need to / don't have to, which are not modal verb forms) when there is no obligation.
  • Contestants don't have to be great actors.
  • You needn't get here before eleven o'clock.
  • We don't have to wear a school uniform.
  • The modal verb need (without to) is only used in the negative. In the affirmative, we use need to (which is not a modal verb) to express necessity.
  • He needs to work harder if he wants to pass his exams.
  • We use ought (not) to, should and shouldn't to give advice and make recommendations.
  • Candidates ought to / should be friendly and outgoing.
  • You ought not to / shouldn't worry about your marks.

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