1.与现在事实相反的虚拟语气,if从句中的谓语用过去式（be用were）,主句用would/could/mightshould+动词原形。
If I had enough money, I would buy myself a computer.
我如果有足够的钱，会为自己买一台电脑。
2.与将来事实相反的虚拟语气，从句谓语过去式（be用were）/should+动词原形/were to+动词原形，主句谓语would/could/might/should do.
If I saw/should see/were to see him tomorrow, I would invite him home.
我如果明天见到他，会邀请他到家里来。
3.与过去事实相反的虚拟语气，主句谓语should/would/could/might+have+过去分词,If 条件从句的谓语形式had+过去分词词。
If we had had enough rain last year,we could have gained a good harvest.
如果去年雨水充足的话，我们可能会有一个好收成。
4. wish后的宾语从句用虚拟语气，从句的谓语形式虚拟情况
与现在事实相反用：过去式（be用were）
与过去事实相反had＋过去分词
与将来事实相反would/ could/might＋动词原形
I wish I could help him. 我希望我能帮助他。
5.would rather后的宾语从句用虚拟语气虚拟情况表示现在或将来的愿望，从句的谓语形式过去式（ be用were）,表示过去的愿望,用had＋过去分词
I would rather you came next Saturday.我宁愿你下周六来。
6 .as if/as though 引导的虚拟语气
as if/as though引导的虚拟语气谓语的形式与wish后的宾语从句的谓语形式一致。
It looks as if it is going to rain. 仿佛天要下雨。（马上就要下雨）
7.if only...句式用虚拟语气
If only I had come to the party yesterday!
要是昨天我来参加聚会就好了！（与过去事实相反）
if only. . 意为“要是······就好了”，其后虚拟语气的用法与wish后的宾语从句的谓语形式一致。
