Advice, necessity, and obligation
For expressing advice we have the modals:
should and ought to (ought to isn't usually used in the negative and interrogative form) to express advice.
need to to express necessity (only in the affirmative form).
needn't (without to) and the don't/doesn't have to are used to make clear there's no need to do something.
must and have to express obligation.
mustn't for expressing prohibition (obligation of not doing)
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