各类状语从句中的虚拟语气用法
英语的动词有三种语气形式，即陈述语气、祈使语气和虚拟语气，陈述语气用来说明事实或就事实提出询问，祈使语气用于表示请求、命令、建议或警告等，而虚拟语气则是谓语动词的一种特殊形式，用来表达假设、猜测、可能或空想等虚拟情况，也可以表示主观愿望或表达某种强烈的感情，通常出现在各类从句中。
 
一. 条件状语从句：
 
时间
 
从句谓语形式
 
主句谓语形式
 
将来
 
if ＋ 主语＋ 动词过去式(be用were)
 
if＋主语＋should + 动词原形
 
if＋主语＋were to + 动词原形
 
主语＋would / should / might / could + 动词原形
 
现在
 
if ＋主语＋ 动词一般过去时
 
主语＋ would / should / might / could + 动词原形
 
过去
 
if＋ 主语＋had done
 
主语＋would / should / might / could have + 动词过去分词
 
例句：
 
1.现在：
 
If I were you，I would choose that picture.
 
2.过去：
 
If you had taken my advice，you would not have made such a mistake.
 
3.将来：
 
If there were a sunny day next Sunday，we would go hiking.
 
二. 目的状语从句：
 
1.在for fear that，in case，lest引导的从句中，若用虚拟语气时，从句谓语为：(should) + do。
 
eg. He started out earlier in case he (should) be late.
 
2.在so that，in order that所引导的目的状语从句中，从句中的谓语为：can / could / may / might / will / would /should + do。
 
eg. He goes closer to the speaker so that he can hear him clearer.
 
三. 原因状语从句：
 
1. should + 原形动词,表现在或将来
 
eg. He was angry that you should call him by name.
 
2. should + 完成式, 表过去
 
eg. I’m very sorry that you should have failed the test.
 
四.方式状语从句：
 
虚拟语气常用于as if, as though 引导的方式状语从句：
 
时间
 
结构
 
主句动作之前
 
had + 过去分词
 
主句动作之后
 
would / could / might / should+动词原形
 
eg. They began to talk warmly as if they had known each other for long.
 
They stopped talking as if someone should come.