Ought is usually followed by ‘to’ and an infinitive: You ought to tell the truth. Sometimes it is used without ‘to’ or a following infinitive in a formal way: ♦ I don’t practise as often as I ought. It is also used in an informal way followed by ‘to’ but no following infinitive: ♦ I don’t spend as much time with them as I ought to.
Ought does not change its form, so the third person singular form does not end in ‘-s’: She ought to try a little harder.
Questions and negatives are formed without ‘do’: You ought not to be here. ♦ Ought I to tell my parents? The negative short form oughtn’t can also be used, and this is less formal.
There is no past tense but ought to have can be used for referring to actions that did not happen but should have, or to actions that have probably happened: I ought to have come earlier. ♦ They ought to have arrived by now.