• Forms
      Ought is a ‘modal auxiliary verb’. The third person singular has no -s.
      She ought to understand.
      We usually make questions and negatives without do.
      Ought we to go now? (NOT Do we ought . . . ?)
      It oughtn’t to rain today.
      After ought, we use the infinitive with to. (This makes ought different from other modal auxiliary verbs.)
      You ought to see a dentist.
  • Obligation
    We can use ought to advise people (including ourselves) to do things; to tell people that they have a duty to do things; to ask about our duty. The meaning is similar to the meaning of should ; not so strong as must .
      What time ought I to arrive?
      I really ought to phone Mother.
      People ought not to drive like that.
  • Deduction
    We can use ought to say that something is probable (because it is logical or normal).
      Henry ought to be here soon — he left home at six.
      ‘We’re spending the winter in Miami. ‘ ‘That ought to be nice.’
  • ought to have . . .
    We can use ought + perfect infinitive to talk about the past. This structure is used to talk about things which did not happen, or which may or may not have happened .
      [ought to + have + past participle]
      I ought to have phoned Ed this morning, but I forgot.
      Ten o’clock: she ought to have arrived at her office by now.