Shall, Should, Ought to
To Offer of Assistance or Polite Suggestion (When you are quite sure of a positive answer)
Shall + subject + base form of the verb
Shall we go for a walk?
Note: Shall is only used with I or we. It is used instead of will only in formal English.
To Offer of Assistance or Polite Suggestion (When you are not sure of a positive answer)
Should + subject + base form of the verb
Should I call a doctor?
A Prediction or Expectation that Something Will Happen
should/shouldn’t + base form of the verb
The proposal should be finished on time.
I shouldn’t be late. The train usually arrives on time.
To Give Advice
should / ought to + base form of the verb
You should check that document before you send it out.
You ought to have your car serviced before the winter.
To Give Advice (about something you think wrong or unacceptable)
shouldn’t + base form of the verb
James shouldn’t teach him words like those.