Used for emphasis to mean "is simply not" or "is definitely not"

Used to ask for permission or to inquire about the possibility of an action, meaning "is it okay?" or "can you?"; literally the "A-not-A" question form of [[可以|可以|ke3 yi3]].

need not; not be really necessary; there is no need at all to do something

must; have to; it is absolutely necessary to

To have no fixed rule or preference; to be flexible or indifferent to whether a thing is done or not