Oughtn't is a spoken form of 'ought not'.
English Easy Learning GrammarModal verbsModal verbs are a particular kind of auxiliary.
Look, I can do it! – Oh yes! So you can.
Can I use your phone? – Of course you can.
Do you think she will ... Read more
English Easy Learning GrammarOught toThe use of ought to is similar to should, but it is much less frequent.
Like should, the verb ought to does not have a past form. It is only used with ... Read more