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
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