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Weaker obligation: should and ought to

Use​

Should and ought to are very similar, and can often replace each other.

  • They ought to be more sensible, shouldn’t they?

They are both used to talk about obligation and duty, to give and ask for advice, and to say what we think it is right for people to do. Should is much more frequent than ought to, especially in negatives and questions.

  • You should/ought to see ‘Daughter of the Moon’ – it’s a great film.
  • You shouldn’t say things like that to Granny.
  • Applications should be sent before December 30th. (More polite than Applications must be sent …)
  • He ought to get a medal for living with her.

In questions, should is used to ask for advice or instructions, like a less definite form of shall (see here).

  • Should I go and see the police, do you think?
  • What should we do?

Should and ought to are not used in polite requests.

  • Could you move your head a bit? I can’t see. (not You should move …)

Past use: should have …​

Should and ought to are not normally used to talk about past obligation. Instead, we can use, for example, was/were supposed to (see here).

  • It was going to be a long day. I was supposed to clean the whole house. (not I should clean …)

But should/ought to have + past participle can be used to talk about unfulfilled past obligations: things which weren’t done, or which may or may not have been done.

  • I should have phoned Ed this morning, but I forgot.
  • Alice ought to have spoken to James, but I’m not sure she did.

ought: forms​

After ought, we use the infinitive with to before other verbs. (This makes ought different from other modal auxiliary verbs.)

  • You ought to see a dentist.

To is not used in question tags.

  • We ought to wake Ella, oughtn’t we? (not … oughtn’t we to?)

Mid-position adverbials (see here) can go before or after ought. The position before ought is more common in an informal style.

  • You always ought to count your change when you buy things.
  • You ought always to count your change … (more formal; rare in AmE)

In American English, interrogative and contracted negative forms of ought to are rare; should is generally used instead.

  • He ought to be here soon, shouldn’t he?

In some English dialects, questions and negatives are made with did (e.g. She didn’t ought to do that), but this structure is not used in standard English.