|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 +|
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.
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.
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.
If had married him, you 虚拟条件句-混合时态 the wife of a gas station attendant.
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.
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.
Had Paul received six more votes in the last election, he would be our chair man now.
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.
“I hope I can spend the rest of my life with you.”
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.
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).
The workers demanded they should be given the wages they should get.
The professor recommended we should look for the information in the library.
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.
should -> 情态动词
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)
could（能） / would（将要） / might(可能) / need（需要） + have done.