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.)

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.