虚拟语气分为：与现在事实相反,与过去事实相反,与将来事实相反
第一种：与现在事实相反,从句用过去时,did或were,主句用would+动词原形
例句:If I were you,I would not study English.
第二种：与过去事实相反,从句用had done,主句是would/could/should have done
例句：If you had come yesterday,you would/should/could have seen her
第三种：与将来事实相反,从句分三种
1、与现在事实相反用法一样
2、were to do
3、should do这里should不可替换,主句用could/would +动词原形
例句
1.If you came tomorrow,you would see me
2.If you were to come tomorrow,you could/would see me
3.If you should come tomorrow ,you could/would see me
这些用法必须是背下来的,没有什么捷径可走,有的时候,阅读里的句子是混杂的,可能主句与过去相反,从句与现在相反,只要熟背我上面所说的,就能分别取从句和主句,加油吧