Question

英语if条件状语从句,我记得老师曾经说过一种用动词过去时的情况,说用过去式表示现在,用现在时表示将

英语if条件状语从句,我记得老师曾经说过一种用动词过去时的情况,说用过去式表示现在,用现在时表示将来,我记不清了,请您指教下

Answer 1

对于主句是将来时，if的从句得用现在时；你说用过去表示现在......是虚拟语气吧：(以下内容纯属复制粘贴)
If虚拟语气
一、 虚拟语气在条件句中的用法
If引导出的条件句中使用虚拟语气时，表示所说的话是非真实的，是一种假设。通常有三种情况，与现在事实相反；与过去的事实相反；与将来的事实相反。
1[/B]、[/B]if从句表示与想在的事实相反的假设时，从句的谓语动词用一般过去时（[/B]be一般用[/B]were），主句用[/B]would/should/could/might+[/B]动词原形[/B][/B]
If we had enough money, we would buy a computer
If I were you,I would take her advice.
If places were a like,there would be little need for geographers.如果各个地方都一样，就不需要地理学家了。
Our life would be better if there were no examination.
2[/B]、[/B]if[/B]从句表示与过去事实相反的假设时，从句的谓语动词用过去完成时，主语用[/B]would/should/could/might+have+[/B]过去分词[/B][/B]
If I had worked harder at school,I would have got a better job.
If he had know your address yesterday,he would have telephoned you.
We might have arrived here eariler if we had taken a taxi.
If it had not been for you help, I would have failed again.
3[/B]、[/B]If[/B]从句表示与将来事实可能相反的假设时，从句的谓语动词用一般过去时，[/B]were to do[/B]或[/B]should+[/B]动词原形，主句用[/B]would/should/could/might+[/B]动词原形[/B][/B]
If it rained tomorrow,we would put off the sports meet.
If he were to leave today,he would get there by Friday.
If she should fail again,we would not blame her.
【注】
（1）有时从句假设过去，而主句假设现在，这时从句用过去完成时，而主句用would/should/could/might+动词原形。
If he had taken my advice,he would be much better now.
（2）if从句中如果有助动词had,should或were时，可以省略if,而从句使用倒装语序。
Had you not left so early,you might have missed the train.
Were I to be young again,I would study medicine.
Should we miss the train,we should have to wait an hour at the station.
（3）有时候假设的情况不是以条件句的形式表示出来，而是用介词without,but for等或是用连词but,or,otherwise等方式来表示的。
Without you help,I wouldn’t have achieved so much,.
But for your help,I would not have succeeded.
We didn’t know his telephone number,otherwise we would have telephone him.
一、 虚拟语气在宾语从句中的用法
1[/B]、动词[/B]wish[/B]后面的[/B]that[/B]从句中常用虚拟语气表示愿望。如果表示现在的愿望，从句中过去时（[/B]be[/B]动词用[/B]were[/B]）；如果表示过去的愿望，从句中用过去完成时或[/B]would/should/could/might+have+[/B]过去分词；如果表示将来的愿望，从句中用[/B]would/should/could/might+[/B]动词原形。[/B][/B]
I wish I know his address.
I wish you had written to him.
I wish I could have slept longer this morning,but I had go get up and come to class.
I wish you would stop asking silly questions.
【注】虚拟语气有时用省略语气，只保留did,had,were,would,could等助动词。
“Have you found the answer to the question?” “I wish I had.”
I can’t go to Anqing with you,but I wish I would.
2[/B]、短语[/B]would rather[/B]后面的宾语从句中要使用虚拟语气表示愿望、后悔。表示现在和将来的愿望时，从句中使用一般过去时；表示对过去事情后悔，从句中用过去完成时。[/B][/B]
I would rather you were happy.
I would rather you came here this Saturday.
I would rather I had seen the professor yesterday.
I would rather you hadn’t blamed her the other day.
3[/B]、表示“建议、要求、命令、决定”的动词（如[/B]suggest,propose,recommend,insist,order,demand,request,advise,command,decide,grant,require,urge[/B]等）后面的[/B]that[/B]从句中要用虚拟语气，谓语动词用“[/B]should+[/B]动词原形”，[/B]should[/B]可省略。[/B][/B]
She suggests that they(should) go there right away.
The author proposed that TV(should) be turned off at least one hour every day.
The captain ordered that his man fire at the enemy.
【注】suggest如作“暗示，表明”解释，其后的that从句中不可用虚拟语气；insist如作“坚持认为”时，其后的that从句中亦不可用虚拟语气
The smile on his face suggested that he was satisfied with our work.
The man insisted that he had never stolen the money.
二、 虚拟语气在主语从句、表语从句或同位语从句中的用法
1、 [/B]在[/B]it is important/necessary/vital/essential/strange that...[/B]句型中用“[/B]should+[/B]动词原形”虚拟式。[/B][/B]
It is important that the meeting be postponed.
It is necessary that she come here twice a week to help clean the room.
It is strange that he should turn down my offer.
2[/B]、在[/B]it is suggested/ required/ requested that...[/B]句型中用“[/B]should+[/B]动词原形”虚拟式。[/B][/B]
3[/B]、句子的主语如果是表示“建议、要求、命令、决定”意义的名词，那么以[/B]that[/B]引导的表语从句中用“[/B]should+[/B]动词原形”虚拟式。[/B][/B]
My idea is that we should think it over before accepting it.
4[/B]、表示“建议、要求、命令、决定”意义的名词后面如果接[/B]that[/B]从句作同位语，那么同位语从句中用“[/B]should+[/B]动词原形”虚拟式。[/B][/B]
We all agreed to his suggestion that we should go to Susong for sightseeing.
She gave the order that no one go out of the house after 10 o’clock.
【注】上述从句中的should均可省略
一、 虚拟语气在状语从句中的用法
1、 [/B]在[/B]as if/as though[/B]引导的状语从句中可使用过去时表示虚拟语气。[/B][/B]
He speaks as if he were on the spot.
She spoke to me as if I were deaf.
This device operated as though it had been repaired.
2、 [/B]在[/B]in case,for fear that,lest[/B]引导的目的状语从句中，常用“[/B]should+[/B]动词原形”虚拟式。[/B][/B]
He left early in case he should miss the last train.
I punished the child lest he should make the same mistake.
3[/B]、在[/B]whether...or...[/B]引导出的让步状语从句中可用动词原形表示虚拟语气。[/B][/B]
Whether it be fine or not,we’ll go ahead with the football match.
It doesn’t matter to me whether he succeed or fail.
二、 虚拟语气在其他情况中的用法
1、 [/B]在[/B]it is (about/high) time (that) ...[/B]句式中，[/B]that[/B]从句中要用一般过去时表示虚拟语气。[/B][/B]
I think it’s time you went to bed.
It’s high time that she made up her mind.
2、 [/B]在[/B]if only...[/B]句式中，谓语动词用过去时表示虚拟语气。[/B][/B]
If only he didn’t drive so fast!
If only she had asked someone’s advice.
If only the rain would stop.
3、 [/B]在一些表示祝愿的话语中，有时用情态动词[/B]may[/B]表示虚拟语气，且句子用倒装；有时还可用动词原形来表示虚拟语气。[/B][/B]
May you have a long and happy life!
Long live the Republic! 共和国万岁！
So be it! 就这样吧！