要考虑的重点问题：时态，单复数，主被动。
概念解释
- 什么是虚拟？
非真实 - 怎么表示虚拟？
把谓语动词改变时态。一反常态，说明表达的事情是虚拟的。 - 虚拟常用于？
if虚拟条件句；名词性从句；情态动词。
变换口诀：从句往前推（往前推一个时态），主句4+1，将来同现在。be一律用were，不用was。
往前推的规则
过去变过去完成，现在变过去。
If 虚拟条件句
| if从句 | 主句 | |
|---|---|---|
| 假设过去 | had done | would + do/have done |
| 假设现在 | did(were) | could should + |
| 假设将来 | did(were)/ were to do/ should do | might + |
假设现在
假设现在：从句往前推（一个时态），主句4加一(would(将要)/could（能够）/should（应该）/might（可能）+ 动词原形)。
情态动词后➕原形
I am not you, so I can’t make the decision.
If I were you, I could make the decision.
I am not a bird, so I can’t fly to you right away.
If I were a bird, I could fly to you right away.
I don’t know his phone number, so I won’t ring him up.
If I knew his phone number, I would ring him up.
He isn’t free at the moment, so he won’t go to the cinema.
If he were free at the moment, he would go to the cinema.
提建议时（If I were you, I should/should/might do sth…）：
–How should the city be run(manage)?
– If I were a mayor, I would make the stressts cleaner and hire more policemen.
If I could(can) rearrange the alphabet, I would put U and I together.
假设过去
过去的事儿应该往前推，推成过去完成时态。
had done, would have done.
Years ago if someone had turned round to me and said “in two years you’ll be England captain”, I would have turned round and said, “I don’t think so!”
He was not student, so he couldn’t attend the lecture.
If he had been a student, he could have attended the lecture.
He didn’t tell her the answer, She didn’t understand it.
If he had told her the answer, She would have understood it.
假设将来
假设将来用的少，因为将来的事情有可能发生。
如果我明天有时间，我就会帮他。(不太可能有时间的情况下，才能用虚拟)
If I had time tomorrow, I would help him.
(were to have/ should have)
If I were to live my life over again, I would have you as my life.
虚拟条件句-混合时态
主句和从句不是同一个时态。
如果过去嫁给他，你就会是一个加油站服务员的妻子。
If had married him, you 虚拟条件句-混合时态 the wife of a gas station attendant.
如果昨天早睡的话，你现在就不会头疼。
If you had slept early yesterday, you would not have a headache.
The room is full of flies because you left the door open. But…
If you hadn’t left the door open, the room would not be full of flies.
I didn’t finish my report yesterday, so I cann’t begin a new project today.
If had finished my report yesterday, I could begin a new project today.
变形应用
省略if的虚拟条件句，从句要倒装，主句不变
倒装：陈述句变一般疑问句。
If you had joined us, we would have had more fun.
Had you joined us, we would have had more fun.
If I were you, I would think it twice.
Were I you, I would think it twice.
If虚拟条件句-省略if
Had Paul received six more votes in the last election, he would be our chair man now.
If虚拟条件句-含蓄的虚拟条件句
With(如果有) better strategy, they would have won the battle.
If they had had a better strategy, they would have won the battle.
Without/But(如果没有) for you help, we couldn’t have succeeded.
If we hadn’t had your help, we couldn’t have succeeded.
But for the English examination, I would have gone to the concert last Sunday.
名词型从句的虚拟语气-wish
名词性从句：句子相当于名词。主、宾、表、同位。
宾语从句的虚拟
1.wish后的宾语从句
“I hope I can spend the rest of my life with you.”
“You wish!”
wish：希望，表示可能性比较小的。
往前推一个时态。
Our classroom doesn’t have any windows. I wish our classroom had windows.
The sun isn’t shining. I wish the sun were shining right now.
I didn’t go shopping. I had gone shopping.
I don’t know how to dance. I wish I knew how to dance.(从句往前推)
You didn’t tell them about it. I wish you had told them about it.
It’s cold today. I am not wearing a coat, I wish I were wearing a coat.
2.表示“建议，要求，命令”的名词性从句
表示“建议，要求，命令”动词后面的从句要虚拟。
应该
变法：从句中用应该(should) + do，should可以省略，无论人称时态。
suggest, advise, propose, recommend.
order, ask, demand, insist,
require, request, …
The engineers proposed (that) they should look at the design again.
The engineers proposed (that) they look at the design again.
He insisted that she should send her sister to a dancing schools.
He ordered they should start the attack before dawn(黎明).
被动形式
The workers demanded they should be given the wages they should get.
The professor recommended we should look for the information in the library.
其他名词性从句
I suggest（宾语从句） that you should work harder.
My suggestion is（表语从句） that you should do sth.
That(主语从句) you should do sth is my suggestion.
Here is my suggestion that you should do sth.
只要是表示建议，命令，要求，不管是名词动词，不管是主语，宾语还是同位语，都要变成should + do.
情态动词的虚拟
should -> 情态动词
情态动词：这个词儿还是动词，只不过不表示任何动作了，而是表示情绪，态度。
can/should/must + do(原形)
should + do (现在应该做，真实)
should + have done (过去应该做某事，过去本来应该做，真实的情况是没做，已经做不了了，虚拟)
shouldn’t + have done (本来不该做，实际上做了)
总结
could（能） / would（将要） / might(可能) / need（需要） + have done.