1、提出将来会发生的事：主句：主语＋would/should/might/could＋动词原形；
从句：should＋动词原形/were to＋动词原形；
2、提出现在的条件： 主句：主语＋would/should/might/could＋动词原形；
从句：动词过去式；
例句：If he studied at this school, he would know the enviornment around the school very much.
3、提出过去的未发生的条件：主句：主语＋would/should/might/could have＋动词过去分词
从句：had＋动词过去分词
例句： If I had read the book, I would have told you about it.
扩展资料
if的用法
if作为从属连词,可引导条件状语从句、让步状语从句和名词从句。
if引导条件状语从句,从句可为真实条件从句,也可为虚拟条件从句。如为真实条件从句,谓语用陈述语气,表示可能性很大,作“假使”“如果”解,通常用一般现在时代替一般将来时; 如果if从句中用will,表示意愿。
从句如为虚拟条件从句,谓语动词要用虚拟语气,表示可能性不大或与过去事实相反,作“要是,假如”解。可指过去的情况,也可指现在和将来的情况。指将来情况时可用were to或should。在现代口语中,一、三人称后常用was代替were。if引导的虚拟条件句中,助动词were,should,had可以移至主语前,此时if可省略。
if引导的条件从句中可以省略be和主语。
if引导的条件从句,有时后接only以加强其语气,表示说话人非常盼望某人提出的条件能够实现。
if可引导让步状语从句,作“虽然,即使”解,常和even连用。
if可引导名词性从句,作“是否”解,常放在ask, doubt, know, learn, see, wonder等动词后。一般用在口语中,而且不能用于句首。
1、提出将来会发生的事：
主句：主语＋would/should/might/could＋动词原形
从句：should＋动词原形/were to＋动词原形
If he should go to Harvard University, he would make full use of his time.
如果他要上哈佛大学的话，他就会充分利用他的时间了。
2、提出现在的条件：
主句：主语＋would/should/might/could＋动词原形
从句：动词过去式
If he studied at this school, he would know the enviornment around the school very much.
如果他在这所学校学习的话，他会很了解周边环境。
3、提出过去的未发生的条件：
主句：主语＋would/should/might/could have＋动词过去分词
从句：had＋动词过去分词
If I had read the book, I would have told you about it.
我如果看过本书，我会把内容告诉你了。
扩展资料
虚拟语气用法：
1、用在含蓄条件句中
句子中，假设的情况不用条件从句表示出来，而是用一个介词短语来表示，句子的谓语形式也可遵循上表的规则。
这种用法也常见于or, or else, otherwise和but后面的分句中。
例如：Without music, the world would be a dull place.
2、用在错综时间条件句中
有时候，条件从句表示的动作和主句表示的动作发生的时间并不一致，这时，谓语动词的形式要根据表示的时间来调整，这种句子可称作错综时间条件句。例如：
If you hadn’t watched television so late, you wouldn’t be so sleepy now.
此句为时间交错的虚拟条件句，从句表示与过去事实相反的假设，主句则假设与现在情况相反
3、用在wish后的宾语从句中
这种句子主要表示愿望，that常省略。若指现在或将来的愿望，从句用过去时;若指过去没有实现的愿望，从句用过去完成时。
例如：I wish I had learned to play chess.(与过去事实相反)
若wish 后的宾语从句中用would，可以表示请求，通常意味着说话人的不快或不满。
例如：I wish you would help us.
4、用在if only感叹句中
当表示“但愿”，“要是…就好”时，它的用法和wish基本相同，只是更富有感情色彩，表示一时很难实现的愿望。
例如：If only I knew what you wanted.
5、用在以as if (as though) 引出的方式状语从句中
当表示过去想象中的动作或情况时，用过去完成时;当表示和现在事实相反或对现在情况有所怀疑时，用一般过去时。
例如：The old couple loved the orphan girl as if she had been their daughter.
6、用在某些虚拟的定语从句中
He was the very person I should have been wished to see.
7、用以表示说话人的主观愿望或选择，仅用在一些惯用句型的从句中
I’d rather they came tomorrow.
但had rather, would rather, would just as soon, would sooner等惯用语如用在简单句中，其后都用不加to的动词不定式。
例如：I’d rather die than give up my principle.
本回答被网友采纳1、提出将来会发生的事：主句：主语＋would/should/might/could＋动词原形；
从句：should＋动词原形/were to＋动词原形；
2、提出现在的条件： 主句：主语＋would/should/might/could＋动词原形；
从句：动词过去式；
例句：If he studied at this school, he would know the enviornment around the school very much.
3、提出过去的未发生的条件：主句：主语＋would/should/might/could have＋动词过去分词
从句：had＋动词过去分词
例句： If I had read the book, I would have told you about it.
扩展资料：
与现在事实相反：If I were you, I would go there tomorrow.
与现在事实相反：If he came to the party, I wouldn't come.
与过去事实相反：If she had been there, she would have met Jack.
与将来事实相反：If it were to rain tomorrow, they couldn't go for an outing.
与将来事实相反：If they should attend the meeting, we might get more support from them.
参考资料来源：百度百科-虚拟语气
本回答被网友采纳1、表示与现在事实相反的情况
从句：If+主语+动词一般过去时(Be动词用were)主句：主语+ should/would/might/could+do：If I were you，I would take an umbrella.如果我是你，我会带把伞。（事实：我不可能是你）
2、表示与过去事实相反的情况
从句：If+主语+had+done主句：主语+should/would/might/could+have done：If I had got there earlier，I should/would have met her.如果我早到那儿，我就会见到她。（事实：去晚了）
3、表示与将来事实相反
从句：①if+主语+were to do
②if+主语+should+do
③if+主语+动词一般过去式（be动词用were）主句:主语+should/would/might/could+do:If he should come here tomorrow，I would talk to him.如果他明天来这儿的话，我就跟他谈谈。（事实：来的可能性很小，不可能）
本回答被网友采纳if虚拟语气的三种时态