ought to

ought to

1. (auxiliary) Indicating duty or obligation.
2. (auxiliary) Indicating advisability or prudence.
3. (auxiliary) Indicating desirability.
4. (auxiliary) Indicating likelihood or probability.

• See ought for fuller examples and usage.
• Many sources consider that ought to is the basic modal verb form. However, many examples of the use of ought without to as a basic modal auxiliary verb are to be found in common use.

• aught
• ought
• Appendix:English modal verbs
• Appendix:English tag questions