unless: conj.

except on the condition that , if… not

Do not leave the building unless you are told/informed/instructed to do so.

Unless the government agrees to give extra money, the theatre will have to close.

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Unless is not used of imaginary events 不能用于假设的事实。Unless cannot be used in this sentence: She would have died unless the doctor had not saved her .

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Unless can only be used instead of “if… not” when there is an idea of ending an intention or situation that already exists只有某种已存在的打算和情况有可能结束或完成之时用。I’ll stay home unless I’m invited.

Not in this sentence: I’ll be angry unless I’m not invited to the

party. Unless 不能用于虚拟语气。