The Verb Ought.
Ought is the past tense of the verb owe, which originally meant ‘to own’, and now means ‘to be under obligation’. Ought always implies duty or obligation. It is followed by a present infinitive or a perfect infinitive.
You ought to consult a doctor about that pain in your knee.
He ought not to have behaved like that.
["ETYMOLOGY: Middle English oughte (1st & 3d singular present indicative), from oughte, 1st & 3d singular past indicative & subjunctive of owen to own"]
["We use ought to have + V3 form to talk about things that were desired or ideal in the past but which didn't happen. It can express regret."]
["The negative form of ought to is ought not to, which is sometimes shortened to oughtn't to in spoken English."]
["The standard construction for the negative is he ought not to have gone: the forms he didn't ought to have gone and he hadn't ought to have gone are not acceptable in standard modern English."]
