文档介绍：条件状语从句
一、真实条件句
谈论将有可能发生的事情，并且考虑其将来的真实结果。主句用一般将来时，从句用一般现在时或其他形式的现在时。
If you help me,I will be grateful.
如果你帮我, 我会感激你 (正常语气)
If it rains, I will not go.
正常语气(不一定会去)
二、虚拟条件句
if从句谈论想象的情况（假设与现在事实相反），主句则推测想象的结果。从句使用一般过去时, 主句使用would+动词原形。尽管这种条件句使用过去时，却并非指过去的时间，所以，if之后的过去时用法常被称为“非真实的过去”，整个条件句也被称作非真实条件句。
If you helped me, I would be grateful.
如果你帮了我, 我会感激你(可惜你没有帮我, 我不会感激你) （虚拟条件句）
If it rained, it would not be hot.
如果下雨类条件句（虚拟条件句） 就不会这么热
If you could make him change his mind, you would save him a lot of trouble.
假如你能使他改变主意, 你会使他免了许多麻烦.
如果if从句中的动词是be, 那么应该在第一和第三人称单数名词之后用were。
If I were you这种说法经常用于提出建议。 If I were you, I’d accept their offer.
If I were in your position, I would act differently.
假如我处于你的位置, 我会采取不同的作法.
虚拟条件句有时也可代替真实条件句来描述颇有可能发生的事情，但比真实条件句较为“无把握”。 If you went by train, you would get there earlier.
If you go by train, you will get there earlier.
虚拟条件句经常用来描写完全不可能的事情。 If I had longer legs, I’d be able to run faster
虚拟条件句的时态
可以表示过去，现在和将来的情况。它的基本特点是时态退后。
1、同现在事实相反的假设。
句型 ： 条件从句 主句
一般过去时 should( would) +动词原形
If they were here, they would help you.
2、表示于过去事实相反的假设。
句型： 条件从句 主句
过去完成时 should (would) have+
过去分词
If she had worked harder, she would have succeeded.
The rice would not have been burnt if you had been more careful.
If my lawyer had been here last Saturday, he would have prevented me from going.
If he had come yesterday, I should / would have told him about it.
含义：He did not come yesterday, so I did not tell him about it.
If he had not been ill and missed many classes, he would have made greater progress.
含义： He was ill and missed many lessons, so he did not make greater progress.
3、表示对将来的假想
句型： 条件从句 主句
一般过去时 should+ 动词原形
were+ 不定式
would + 动词原形
should+ 动词原形
If you succeeded, everything would