1、表示现在的虚拟式
与现在事实相反
从句：动词的过去式（be的过去式一般用were） 主句：would/ should/ could+ 动词原形
与过去事实相反
从句：had + 过去分词 主句：would/ should/ could + have + 过去分词
与将来事实相反
从句：动词过去式，should + 动词原形，were to + 动词原形 主句：would/ should/ could + 动词原形
If I were a bird, I would fly to you.
2、表示过去的虚拟式
与现在事实相反
从句：动词的过去式（be的过去式一般用were） 主句：would/ should/ could + 动词原形
与过去事实相反
从句：had + 过去分词 主句：would/ should/ could + have + 过去分词
与将来事实相反
从句：动词过去式，should + 动词原形，were to + 动词原形 主句：would/ should/ could + 动词原形
If she hadn’t been ill, she might have come.
3、表示将来的虚拟式
与现在事实相反
从句：动词的过去式（be的过去式一般用were） 主句：would/ should/ could + 动词原形
与过去事实相反
从句：had + 过去分词 主句：would/ should/ could+ have + 过去分词
与将来事实相反
从句：动词过去式，should + 动词原形，were to + 动词原形 主句：would/ should/ could+ 动词原形
If Professor Li should have time tomorrow, we could ask him some questions.
