虚拟语气:：表示所说的内容与事实不符,不是事实或是不可能发生的,只是
一种愿望,建议或与事实相反的假设等.
真实条件句
真实条件句用于陈述语气,假设的情况可能发生,其中 if 是如果的意思.
时态关系
句型：条件从句 主句
一般现在时 shall/will + 动词原形
If he comes,he will bring his violin.
典型例题
The volleyball match will be put off if it ___.
A.will rain B.rains C.rained D.is rained
答案B.真实条件句主句为将来时,从句用一般现在时.
非真实（虚拟）条件句
1）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.
a.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.
b.表示与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.
c.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 be all right.
If you should succeed,everything would be all right.
If you were to succeed,everything would be all right.
wish的用法
用于wish后面的从句,表示与事实相反的情况,或表示将来不太可能实现的愿望.其宾语从句的动词形式为：
真实状况 wish后
从句动作先于主句动词动作 现在时 过去时
（be的过去式为 were）
从句动作与主句动作同时发生 过去时 过去完成时
（had + 过去分词）
将来不大可能实现的愿望 将来时 would/could +
动词原形
I wish I were as tall as you. 我希望和你一样高.
He wished he hadn't said that.他希望他没讲那样的话.
I wish it would rain tomorrow.我希望明天下雨就好了.