adj.紧要的；必要的；祈使的
n.紧要的事；命令；义务；驱使
It is imperative that we make a quick decision. 我们要尽快做出决定。
It's imperative that you apologize to him immediately. 你必须立即向他道歉。
"Go!" is in the imperative mood. “Go！”是祈使语气的句子。
用作名词 (n.)Everyone should fulfill their social imperatives earnestly. 每个人都应认真履行其社会职责。
imperative用作形容词的基本意思是“必要的,紧急的,极重要的”,在句中多用作表语,在“It is/was imperative that-clause”结构中从句的谓语动词多用虚拟式,英式英语中常用“should+动词原形”,而在美式英语中则常省略should。
