I was confused by usage of be supposed to and ought to modals. Where can we use them? For instance, I am supposed to/ought to learn English today. I don't have to learn english today, but to me it would be very useful if I learned English today because I could improme my skill. I suspuect that ought to is more suitable here, isn't it?

Another example, I ought to/am supposed to meet my friend in the railway station today. Here is more suitable am supposed to, because it would be amoral if I didn't meet my friend, especially if ti has been arranged earlier.

Is it correct? I'd like you explain me those constructions in details, please :)

  • 'Be supposed to' gives a nod to an external arbiter of standards, even if only probable public opinion (We're supposed to spend at least two hours on our homework). 'Ought to' references rather a code of ethics or at least known best practice (I ought to eat less fat). Commented Mar 29, 2015 at 15:30

1 Answer 1


"be supposed to do something", is required to do something because of one may find himself in a situation, or put himself in a situation: agreement, promise, and lack of authority if the usage in negative form: "I am not supposed to remove these books from the reference room". It is an idiomatic expression not a modal. Modal verbs are must, shall, will, should, would, can, could, may, and might.

must, and have to are a lot stronger, the strongest is 'must'. and there is 'should' in between have to and supposed to do.

You must obey the law.

shall expresses strong assertion, and promise in a positive form; in the negative, a command, a divine order; thou shan't steal!

In the interrogative shall expresses an offer, " Shall I pick you up in the airport?"

ought to, comes close to should, as it indicates duty, and correctness.

Your usage is by the book.

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