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The antonym of "ought" in the sense of should is "shouldn't" or "ought not:"
"Jack ought to have joined in the fun."
"No, he shouldn't have joined in if it wasn't fun for him."
'Ought to be' is present tense. 'Ought to have been' is past tense.
You ought to have this question answered by now!
He ought to stay focused on his goals in order to achieve success.
It has one syllable.