Ought was originally the past tense of owe, but now it refers to present and future time. Ought is different from other auxiliaries in that it is followed by an infinitive with to.

• You ought to do it. (NOT You ought do it.)

Ought is not as forceful as must, but it is stronger than should.

Uses
Ought expresses ideas such as duty, necessity and obligation.

• You ought to work hard.
• He ought to go.
• Students ought to respect their teachers.
• You ought to be punctual.

• I ought to buy some furniture.

Ought can refer to the past when it is used with the present perfect of the principal verb.

• He ought to have asked my opinion.
• We ought not to have wasted so much time over it.

Related posts:

1. Uses of Must
2. Uses of Should
3. Modal Auxiliaries
4. Uses of Have
5. Uses of Do
6. Modal auxiliary verb shall
7. Modal Auxiliary Verb Will
8. Uses of Could
9. Modal Auxiliary Verb Would