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.
