2、must have done sth：表示对过去内容的肯定性的推测。

　　例：1、Mr Green must have failed to receive my letter, otherwise he would have replied.

　　2、I believe he must have had an accident, otherwise he would have arrived on time.

　　一、虚拟语气的基本内容

　　根据虚拟与其这种与事实相反的假设所对应的时间不同，虚拟语气的if虚拟条件从句与主句的谓语动词分别有三类构成形式：

　　假设类型If虚拟条件从句

　　主句与现在事实相反 Did/were Would/should do 与过去事实相反 Had done Would/should have done 与将来事实可能相反 Were to do/did/should do Would/should do

　　例：1、I wouldn't talk that way if I were Peter.

　　2、If the whole operation had not been planned before hand, a great deal of time and money

　　would have been lost

　　3、Jean doesn't want to work right away because she thinks that if she were to get a job she probably wouldn’t be able to see her friends very often.

　　4、I would ask George to lend us the money if I knew him.

　　5、Do you think there would be less conflict (战斗、斗争) in the world if all people spoke the same language.

　　6、If Bob had come with us, he would have had a good time.

　　二、if的省略形式(又称虚拟语气的倒装结构)

　　在if虚拟条件从句中，如果谓语部分包含were，should，had等词，则可以把这些词放到主语前，省略if，构成虚拟语气的倒装结构。

　　三、主句与从句时间不一致时虚拟语气的构成

　　当虚拟语气的if虚拟条件从句和主句的动作发生的时间不一致时，要根据各自表示的时间采用对应的虚拟语气的构成形式。

　　例：1、If I had attended the meeting yesterday, I would know what happened now.

　　2、If you had taken our advice at that time, you would not be in trouble now.

　　四、主观倾向性动词引导的虚拟语气的构成

　　在英语中存在一些动词，表示建议、命令、要求等主观的倾向，由这些动词引导的that宾语从句中，从句的谓语动词要用should+动词原形，should可以省略。这类常见的主观倾向性动词有“一坚持、二命令、三建议、五要求”，分别是： (责任编辑：admin)