虚拟语气用来表达不可能或难以实现的愿望，与事实相反的假设，通常分为基本的三种形式。

1. 与现在事实相反的虚拟：
If did / were ..., ... would/ should/ could/ might  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.)

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2. 与过去事实相反的虚拟：
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 little earlier just now, you might have met her.  (You didn't come here earlier.)

3. 与将来事实相反的虚拟：
(1) If should v., ... would v.   （可能性很小）（译作“万一”）
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.  （完全不可能）
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.

4. 金牌特殊重点

［简单联想记忆］：
● 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.
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。此类常见的名词有：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）
had done（指过去）
would v.（指将来）
I wish that I met my uncle now.
I wish I had met my uncle yesterday.
I wish I 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.

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