Modal verb: Ought to

"..People ought to know several things about the recent history.."





Ought is different from other auxiliary verbs. It is used with to.
We can use ought to instead of should in some contests.
example:
- Do you think I ought to apply for this course in particular?
- Yesterday it was a useful lesson in the university. You ought to have come.
- He has been studying hard for the exam, so he ought to pass.

Ought expresses duty, necessity, desirability and similar ideas. It is often used to advise people: to tell them that they have a duty to do things. The meaning is similar to should, is not as forceful as must. 
examples:
- You ought to attend school regularly. (Duty)
- You ought to help the needy. (Moral obligation)
- We ought to buy a new car, the other one has broken down. (Necessity)


NOTE:
Note that to is dropped in question tags.
- You ought to love your girlfriend, ought not you? (NOT…ought not you to.) 

Ought does not have infinitives (to ought) or participles (oughting, oughted). Questions and negatives are made without do.


BUT:
Ought is rarely used in questions and negatives; should is generally used instead. A structure with think … ought is also common.
examples:
- We ought to help them, shouldn’t we? (More natural than ought not we?)
- Do you think I ought to consult a doctor? (More natural than Ought I to consult a doctor?) 
- Should we tell her? (Less formal than Ought we to tell her?)