说到虚拟语气，好多人开始头大，感觉不知所措，造成这种感觉的主要原因是学习时不够系统，分类不明确。

一、 虚拟语气的定义：

英语中的语气分为陈述语气、祈使语气、虚拟语气三类。虚拟语气用来表示假想，而不表示客观存在的事实，所说的是一个条件，不一定是事实，或与事实相反。另外表示主观愿望或表达某种强烈的感情时，也可用虚拟语气。

虚拟看似繁复，但虚拟语气的应用其实只分为三类——状语从句中的虚拟，宾语从句中的虚拟和定语从句中的虚拟，这三类虚拟语气的标志性用词，分别是if，wish和It is time that…，其它虚拟语气的形式都可以视为是这三个标志词典型用法的延伸。

二、 if引领的状语从句中的虚拟语气：

1真实条件句

状语从句2中，我们讲了应用最为普遍的虚拟语气——“主将从现”，如：

If it doesn’t rain tomorrow, I willgo back home.

明天有可能下雨，条件为真实，即真实条件句，使用“主将从现”；但有时条件非真，if引领的条件句的时态，就要根据不同的假设条件，进行相应的时态上的变化。

2非真实条件句

①表示对话中的假设或与现在事实相反：

从句：If+主语+一般过去时(be动词用were)

主句：主语+ should/would/might/could + do：

If I were you，I would take an umbrella.

If I knew his telephone number，I would tell you.

②表示与过去事实相反的情况

从句：If+主语+had+done

主句：主语+should/would/might/could+have done

If I had got there earlier，I should/would have met her.

意为没有早到，如果早到，我本可以见到她。

If he had taken my advice，he would not have made such a

mistake.

意为没有听劝告，如果听劝告，本不该犯这样的错误。

③表示与将来事实相反

从句：if+主语+were to do

   if+主语+should + do

主句：主语+should/would/might/could + do

If he should come here tomorrow，I would talk to him.

If she were to be here next Monday，I would tell her about the

matter.

意为来的可能性很小，几乎不可能。

总结如下：

注意：

1.有时，虚拟条件句中，如果主句和从句的谓语动作若不是同时发生时，虚拟语气的形式可作相应调整，即错综条件句，错综条件句的使用，主要以作者想要表达的意思为主，一般来说，没有语法上的强制要求。

①从句的动作与过去事实相反，而主句的动作与正在发生的事实不符。

If I had worked hard at school，I would be anengineer now.

If they had informed us，we would not come here now.

②从句的动作与现在事实相反，而主句的动作与过去事实不符。

If he were free today，we would have sent him to Beijing.

If he knew her，he would have greeted her.

2.当从句的谓语动词含有were，should，had时，if可以省略，这时从句可用倒装语序，即把were，should，had等词置于句首，多用于书面语。Should he agree to go there，we would sendhim there.

= If he should…

Were she here，she would agree with us.

= If she were here…

Had he learnt about computers，we would have hired himto work here.

= If he had learnt…