If + did / were + ……, …… would
could + do (动词原形)
If I were you, I would go abroad at once. (I am not you.)
If he knew it now, he could help me. (He doesn't know it now.)
If + had done + ……, …… would (might) have done ……
If I had known your telephone number yesterday, I would have phoned you.
(I didn't know your telephone number.)
If you had come here a littleearlier just now, you might have met her.
(You didn't come here earlier.)
(1) If + should + v, …… would + v.
If it should rain tomorrow, you could stay at home.
If I should fail, what should Ido?
(2) If + did / were to + v ……, would + v.
If the sun were to rise in the west, I would lend you the money.
If you finished it in 3 minutes, I would give you my car.
● 下列动词后的“宾语从句”中需要用虚拟形式，即should + 动词原形，shoud在美国英语中要省略(TOEFL语法考点)。此类常见的动词有
：order, ask, decide, demand, require, recommend, suggest(建议)insist(坚决要求)，advise, etc.
例句：He suggested that we (should) help them with English.
The teacher ordered that the homework (should) be finished within half an hour.
● 下列名词后的同位语从句中要用“should + 动词原形”(should可省去)的虚拟。
suggestion, order, request, demand, importance, proposal.
He made a suggestion that we (should) have a fancy dress party.
I think it is a thing of importance that it (should) be done soon.
● It is / was important / necessary / natural / essential / advisable / strange / surprising, ect. + that +主语+ should + v.
It is strange that you should say such a thing.
It was important that you should tell me all the information.
● wish后的宾语从句中，as if 后的状语从句中，须用下列的虚拟形式：
主 + wish+ (that) + 主 + did / were(指现在)
Iwishthat I met my uncle now.
IwishI had met my uncle yesterday.
IwishI could meet my uncle tomorrow.
● It is (high) time that …… + did / were ……
It is time that you went to bed.
● would rather that …… + did / were ……
I would rather that you were not here now.
● would sooner that …… + did / were ……
I would sooner that you got up earlier.
I would sooner that you were not my brother.