虚拟语气是说话人表达的一种主观愿望，假设或建议等。

一、if 引导的非真实条件的虚拟语气

二、虚拟语气的省略

当虚拟条件句的谓语动词含有were，should，had时，if可省略，而将were，should，had等词置于句首。

【例】Were she here,she would agree with us.

三、混合虚拟语气

有时候虚拟条件中，主、从句的动作若不是同时发生时，须区别对待。

1.从句的动作与过去事实相反，而主句的动作与现在事实不符。

If i had worked hard at school,i would be an engineer,too.

如果我在学校努力学习的话，我现在也会是工程师了。

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 being,

如果他今天有空的话，我们会已经派他去北京了。

3.从句的动作与过去发生的情况相反，而主句的动作与现在事实不符。

If it had not been raining too much,the crops would be growing much better.

如果天不下太多雨的话，庄稼会长的更好。

含蓄虚拟语气常用来表示虚拟条件的介词有but that , but for, without, or,otherwise等等，它们表示的虚拟条件都可以替换if从句。

对现在/将来的虚拟：would/could+do对过去的虚拟：would/could+have done

【例句】But that i saw it (=if i had not seen it) ,i could not have believed it

要不是亲眼看见的话我是不会相信的

should+do 引导的虚拟语气动词后的宾语从句:表示主观判断，推测，建议，命令和要求的动词通常引起虚拟的宾语从句，此类动词后的宾语从句中采用：“(should)+do”虚拟语气的形式。

此类有：advise,ask,demand, insist,order, propos,request,suggest,require,urge,desire,command,recommend等此类动词的名词、形容词形式，以及过去分词形式引导的同位语从句和表语从句也要虚拟。

it is/was+形容词+从句的结构中，从句的谓语动词用(should)+do表虚拟这些词有:important, vital, necessary, crucial, key, strange,essential,natural,imperative, possible, probable

由lest,in case,for fear that引导的目的状语从句，

从句的谓语动词用(should)+do表虚拟

wish引导的虚拟语气对现在的虚拟：动词过去式(be用were)

对过去的虚拟：过去完成时(had done)或情态动词(would/could)+have done

对将来的虚拟：情态动词(would/could)+do

would rather/sooner/as soon引导的虚拟语气

对现在和将来的虚拟：did/were

we’d rather you went here tomorrow

对过去的虚拟：had done

I‘d rather you had seen the film yesterday.

It is+(high/about)time+(that)引导的虚拟语气

it is time that i went to pick up my daughter at school

as if/as though 和if only引导的虚拟语气

对现在的虚拟：动词过去式(be用were)

对过去的虚拟：过去完成时(had done)

They began to talk warmly as if they had known each other for long.

对将来的虚拟：情态动词(would/could)+do

He coughed twice as if someone would come.