Modal Verbs – Part 3


‘Should’ is the past form of ‘shall’: ‘I shall take the train to Colchester.’ (present: resolution) – ‘I thought I should take the train to Colchester.’ (past). ‘Shall’ is a rather old-fashioned word and we generally prefer to use ‘will’ instead: ‘I will take the train to Colchester.’

Modal perfect: ‘should have’ means an action that the speaker feels would have been good in the past, but did not happen: ‘I should have watched the match, but I didn’t.’

‘Ought to’ has the same meaning as ‘should’. ‘You should be nicer to Derek.’ – ‘You ought to be nicer to Derek.’ …and so on. It’s fair to say that ‘should’ is more common and less formal than ‘ought to’. We might use ‘ought to’ to give more emphasis than ‘should’, because it gives us two strong stressed syllables instead of one: ‘You really ought to tidy up in here!’ compared with: ‘You really should tidy up in here!’


‘May’ and ‘might’ mean the same thing and can be used interchangeably. The formal permission use (above) is less common nowadays. Instead of saying ‘Might I leave early today’ we would probably ask, ‘Can I leave early today?’

In the meaning of ‘formal permission’, the past of ‘may’ and ‘might’ is constructed from the verb ‘to be allowed to’, for example:

‘You were allowed to leave early yesterday.’ (past) – ‘You might leave early today.’ (present) – ‘You will be allowed to leave early tomorrow.’

Modal perfect: ‘might have’ / ‘may have’ means an action that the speaker feels was possible in the past, but cannot be proven beyond doubt: ‘I may have seen Jamie at the station, but I can’t be sure.’



‘Must’ has no past or future form. We use ‘had to’ in the past and ‘will have to’ in the future. However, ‘must’ can have a future meaning, for example:

  • ‘I had to phone my mother.’ (past)
  • ‘I must phone my mother.’ (present form, with future meaning: it is my intention to do this in the near future)
  • ‘I will have to phone my mother.’ (future)

The difference between ‘must’ and ‘have to’ is that the action in ‘must’ originates from an internal instinct or feeling that is often personal – ‘I must give up smoking’ – while the action in ‘have to’ is often decided by an external agent and therefore may concern rules, laws, teachers, bosses, punishment… things that you do not necessarily want to do, but have to do. For example:

The negative form of ‘must’ is ‘do not have to’ (see above) – not ‘must not’, which means prohibition – that you are not allowed to do something. The opposite of prohibition is permission, so (rather confusingly) we use ‘can’ as the negative form of ‘must not’:

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