2024届高考英语复习条件句讲义
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条件句
概说
条件句指某一事情发生后其他事情始能发生。if的意思是“假如”。如：
If the rain stops, we’ll be able to go for a walk.
如果雨停了，我们就能去散步了。
if引导的条件状语从句指能够发生、可能发生、或者可能发生过的事情。有时事情发生的可能性很大：
If the price of oil comes down, more people will buy it.
如果油价下跌，就会有更多的人购买。
有时候事情没有可能发生：
If my horse had won, I would have made a lot of money.
如果我的马赢了，我早就赚很多钱了。
条件句经常由if来引导，但是还有其他词可以引导条件句。条件句也可能是含蓄的，也就是没有条件从句：
I wouldn’t go that way. (含蓄条件句是If I were you如果我是你的话)
我不会走那条路
条件句有三种类型，每一类又有许多变体。其基本构成如下：
第一类：if+现在时， +will do →十分可能的事情
If I lose my job, I will go aboard.
如果我失业了，我就出国。
第二类：if+过去时， +would do →想象现在的情况
If I lost my job, I would go aboard.
假如我失业了，我就出国。
第二类：if+过去完成时， +would have done →想象过去的情况
If I had lost my job, I would have gone aboard.
假如当初我失业了，我就已经出国了。
will可以写作’ll，在I和we之后可以由shall来代替；
would可以写作’d，在I和we之后可以由should来代替。
在条件句中可以混合运用以上三类条件句：
If I am as clever as you think, I would have been rich by now.
如果我像你想象的那样聪明，我现在应该很富有了。
If you knew me better, you wouldn’t have said that.
如果你更了解我，你就不会这么说了。
If I had had your advantages, I would be better off now.
如果我有你的优势，我现在会过得更好。
If he missed the bus, he won’t be here on time.
如果他没赶上公共汽车，他就不能准时到这儿了。
第一类条件句 (真实条件句)
基本结构
if+现在时，will do
在第一类条件句中，所有的现在时都可以用在从句中，不仅仅是一般现在时。对主句来说，也是同理，可以是will do、will be doing、will have done、will have been doing。
注意，will表示愿意、某人特有的习惯时，也就是不表示将来、而用作情态动词时，也可以用在从句中。
If you will wait a moment, I will fetch the money.
如果你肯稍等一会，我就去拿钱。
变体I
if + 现在时， 情态动词:
If she finishes early, she can phone me.
如果她早点结束，她可以给我打电话。
主句中的will表示接近100%的肯定，如果达不到，或者是想表达其他意思就可以使用别的情态动词来代替will。
变体II
if + (should) do, 祈使句：
If you (should) see him, please give him me regards.
如果你见到他，请代我问候他。
句子中的should可以省略，常用在礼貌地提出请求或者圆通地告诉别人该做什么的时候。也就是说，从句中的主语通常是you。主句并非一定是祈使句，祈使句也能用在普通的条件从句中。从句的否定式是don’t+动词原形，否定式不能带should（用should起始句子除外）。
If you don’t see him,… (√) If you shouldn’t see him,… (×)
在这种变体中，可以用should起始句子。这种用法更加正式、语气更加委婉:
Should you not wish out agent to call, please let us know.
如果您不希望我们的代理人打电话，请告诉我们。
这就是唯一一种用should的否定式。
像if necessary(如果需要的话), if possible(如果可能的话), if so(如果这样的话)这样，实际上是省略了的if从句。完全形式是if it (should) be necessary, if it (should) be possible, if it (should) be so。这是虚拟语气的一种。
第二类条件句
基本结构
if+一般过去时，+would do
If you could see me now, you’d laugh your head off.
如果你现在能看到我，你会笑得前仰后合的。
注意，在第二类条件句中的从句中的not不是否定的意思：
I wouldn’t be surprised if he didn’t try to blackmail you. (= if he tried to blackmail you)
如果他想讹诈你，我也不会感到惊讶。
第二类条件句用来想象的情况，尽管从句使用过去时，但是并不表示过去。其经常被用来表示完全不可能的事情：
If I had longer legs, I’d be able to run faster.
如果我的腿再长点，我就能跑得更快。
但是也可以用第二类条件句代替第一类条件句描述有可能发生的事情：
If you go by train, you will get there earlier.
If you went by train, you would get there earlier.
如果你坐火车去，你会更早到达那里。
以上两句意思是一样的，但是后者较为无把握。
变体I
if + were, would
If you were ready, we would go.
如果你准备好了，我们就出发。
If I were sb/If I were in one’s position 用来提建议：
If I were you, I’d accept their offer.
If I were in your position, I’d accept their offer.
如果我是你，我会接受他们的提议。(你应该接受他们的建议)
If it were not for/ Were it not for 用来说明某事发生与否的原因：
If it weren’t for your help, I would still be homeless.
Were it not for your help, I would still be homeless.(更加正式)
如果不是你的帮助，我仍然会无家可归。
变体II
if+过去时， 情态动词（could, might, should）
如果想象的结果可能性更小、或者指能力的时候，可以用以上三个情态动词代替。could表示能力，might表示更小的可能性，should表示应该。
If he knew the facts, he could tell us what to do.
如果他知道事情真相，他可以告诉我们该怎么办。
If she were here, she might help us.
如果她在这里，她可能会帮助我们。
If Ken failed, he should try again.
如果肯失败了，他应该再试一次。
变体III
If + were to do, would
在第二类条件句中，可以用were to do代替一般过去时。这种从句没有否定结构。
If I were to ask, would you help me
如果我请求，你能帮我吗？
如果句子用were开头，会显得非常正式：
Were the government to cut Value Added Tax, prices would fall.
如果政府削减增值税，价格才会下跌。
这种倒装结构有否定形式：
There’d be a clear case for legal action over this matter were it not likely to make life difficult for all of us.
要不是会造成我们全体生活上的困难，我们是完全有理由对此事提起诉讼的。
第三类条件句（假设条件句）
基本结构
if + 过去完成时， would have done.
If it had been raining this morning, we would have stayed at home.
如果今天早上一直下雨，我们就会呆在家里了。
If I could have stopped, there wouldn’t have been an accident.
如果我能停下来，就不会发生事故了。
if从句中不使用would have done, should have done。
第三类条件句表示想象的事情，这和第二类条件句相似。但是第三类条件句永远不可能发生，因为第三类条件句描述的是与过去相反的事情。
在第三类条件句中，had可以倒装：
Had the management acted sooner, the strike wouldn’t have happened.
如果管理层早点采取行动，罢工就不会发生了。
if I had been sb/ if I had been one’s position 用来描写站在他人立场可能会采取的行动
If I had been you, I’d have accepted their offer.
If I had been in your position, I’d have accepted their offer.
如果我是你，我早就接受他们的提议了。（你本该接受他们的建议）
if it hadn’t been for 用来接收为什么某事在过去没有发生：
If it hadn’t been for the rain, we would have had a good harvest.
如果不是因为下雨，我们本会有一个好收成。
Had it not been for the unusually bad weather, the rescue party would have been able to save the stranded climber.
如果不是因为天气异常恶劣，救援队本可以救出被困的登山者。
变体I
if+过去完成时， 情态动词（could, might, should）+have done
如果想象的结果可能性更小、或者指能力的时候，可以用以上三个情态动词代替。could表示能力，might表示更小的可能性，should表示应该。
If he had been here yesterday, he could have told us.
如果他昨天在这里，他本可以告诉我们的。
If he had received a present, he should have thanked her.
如果他收到了礼物，他应该感谢她。
If he had been here, he could have been helping us in the shop.
如果他在这里，他可能会在商店里帮助我们。
含蓄条件句
含蓄条件句指不含if，unless的条件句。
With luck (= if we are lucky) , we’ll be there by tomorrow.
如果运气好的话，我们明天就会到那里。
Given time (= if we give them time), they’ll probably agree.
如果我们给他们时间，他们可能会同意的。
To hear him talk (=if you could hear him talk), you’d think he was Prime Minister.
听他讲话，你会以为他是首相哩。
I would write to her, but I don’t know her address (=if I knew her address).
我会写信给她，但我不知道她的地址。
But for his pension (= if he didn’t have his pension), he would starve.
如果没有退休金，他就会饿死了。
Without your help ( = if you hadn’t helped), I couldn’t have done it.
如果没有你的帮助，我不可能做成这件事。
In different circumstances (= if circumstances had been different), I would have said yes. 如果情况不同，我会答应的。
if的其他含义
if表示当……时（=when）
If it rains heavily, our river floods. 每当下大雨时，我们这条河流就泛滥。
if意谓when时指永久性的真理。主句的时态可以是用will，也可以用一般现在时。
If you boil water, it turns/will turn into steam.
你把水烧开，水就变成气态。
概说
条件句指某一事情发生后其他事情始能发生。if的意思是“假如”。如：
If the rain stops, we’ll be able to go for a walk.
如果雨停了，我们就能去散步了。
if引导的条件状语从句指能够发生、可能发生、或者可能发生过的事情。有时事情发生的可能性很大：
If the price of oil comes down, more people will buy it.
如果油价下跌，就会有更多的人购买。
有时候事情没有可能发生：
If my horse had won, I would have made a lot of money.
如果我的马赢了，我早就赚很多钱了。
条件句经常由if来引导，但是还有其他词可以引导条件句。条件句也可能是含蓄的，也就是没有条件从句：
I wouldn’t go that way. (含蓄条件句是If I were you如果我是你的话)
我不会走那条路
条件句有三种类型，每一类又有许多变体。其基本构成如下：
第一类：if+现在时， +will do →十分可能的事情
If I lose my job, I will go aboard.
如果我失业了，我就出国。
第二类：if+过去时， +would do →想象现在的情况
If I lost my job, I would go aboard.
假如我失业了，我就出国。
第二类：if+过去完成时， +would have done →想象过去的情况
If I had lost my job, I would have gone aboard.
假如当初我失业了，我就已经出国了。
will可以写作’ll，在I和we之后可以由shall来代替；
would可以写作’d，在I和we之后可以由should来代替。
在条件句中可以混合运用以上三类条件句：
If I am as clever as you think, I would have been rich by now.
如果我像你想象的那样聪明，我现在应该很富有了。
If you knew me better, you wouldn’t have said that.
如果你更了解我，你就不会这么说了。
If I had had your advantages, I would be better off now.
如果我有你的优势，我现在会过得更好。
If he missed the bus, he won’t be here on time.
如果他没赶上公共汽车，他就不能准时到这儿了。
第一类条件句 (真实条件句)
基本结构
if+现在时，will do
在第一类条件句中，所有的现在时都可以用在从句中，不仅仅是一般现在时。对主句来说，也是同理，可以是will do、will be doing、will have done、will have been doing。
注意，will表示愿意、某人特有的习惯时，也就是不表示将来、而用作情态动词时，也可以用在从句中。
If you will wait a moment, I will fetch the money.
如果你肯稍等一会，我就去拿钱。
变体I
if + 现在时， 情态动词:
If she finishes early, she can phone me.
如果她早点结束，她可以给我打电话。
主句中的will表示接近100%的肯定，如果达不到，或者是想表达其他意思就可以使用别的情态动词来代替will。
变体II
if + (should) do, 祈使句：
If you (should) see him, please give him me regards.
如果你见到他，请代我问候他。
句子中的should可以省略，常用在礼貌地提出请求或者圆通地告诉别人该做什么的时候。也就是说，从句中的主语通常是you。主句并非一定是祈使句，祈使句也能用在普通的条件从句中。从句的否定式是don’t+动词原形，否定式不能带should（用should起始句子除外）。
If you don’t see him,… (√) If you shouldn’t see him,… (×)
在这种变体中，可以用should起始句子。这种用法更加正式、语气更加委婉:
Should you not wish out agent to call, please let us know.
如果您不希望我们的代理人打电话，请告诉我们。
这就是唯一一种用should的否定式。
像if necessary(如果需要的话), if possible(如果可能的话), if so(如果这样的话)这样，实际上是省略了的if从句。完全形式是if it (should) be necessary, if it (should) be possible, if it (should) be so。这是虚拟语气的一种。
第二类条件句
基本结构
if+一般过去时，+would do
If you could see me now, you’d laugh your head off.
如果你现在能看到我，你会笑得前仰后合的。
注意，在第二类条件句中的从句中的not不是否定的意思：
I wouldn’t be surprised if he didn’t try to blackmail you. (= if he tried to blackmail you)
如果他想讹诈你，我也不会感到惊讶。
第二类条件句用来想象的情况，尽管从句使用过去时，但是并不表示过去。其经常被用来表示完全不可能的事情：
If I had longer legs, I’d be able to run faster.
如果我的腿再长点，我就能跑得更快。
但是也可以用第二类条件句代替第一类条件句描述有可能发生的事情：
If you go by train, you will get there earlier.
If you went by train, you would get there earlier.
如果你坐火车去，你会更早到达那里。
以上两句意思是一样的，但是后者较为无把握。
变体I
if + were, would
If you were ready, we would go.
如果你准备好了，我们就出发。
If I were sb/If I were in one’s position 用来提建议：
If I were you, I’d accept their offer.
If I were in your position, I’d accept their offer.
如果我是你，我会接受他们的提议。(你应该接受他们的建议)
If it were not for/ Were it not for 用来说明某事发生与否的原因：
If it weren’t for your help, I would still be homeless.
Were it not for your help, I would still be homeless.(更加正式)
如果不是你的帮助，我仍然会无家可归。
变体II
if+过去时， 情态动词（could, might, should）
如果想象的结果可能性更小、或者指能力的时候，可以用以上三个情态动词代替。could表示能力，might表示更小的可能性，should表示应该。
If he knew the facts, he could tell us what to do.
如果他知道事情真相，他可以告诉我们该怎么办。
If she were here, she might help us.
如果她在这里，她可能会帮助我们。
If Ken failed, he should try again.
如果肯失败了，他应该再试一次。
变体III
If + were to do, would
在第二类条件句中，可以用were to do代替一般过去时。这种从句没有否定结构。
If I were to ask, would you help me
如果我请求，你能帮我吗？
如果句子用were开头，会显得非常正式：
Were the government to cut Value Added Tax, prices would fall.
如果政府削减增值税，价格才会下跌。
这种倒装结构有否定形式：
There’d be a clear case for legal action over this matter were it not likely to make life difficult for all of us.
要不是会造成我们全体生活上的困难，我们是完全有理由对此事提起诉讼的。
第三类条件句（假设条件句）
基本结构
if + 过去完成时， would have done.
If it had been raining this morning, we would have stayed at home.
如果今天早上一直下雨，我们就会呆在家里了。
If I could have stopped, there wouldn’t have been an accident.
如果我能停下来，就不会发生事故了。
if从句中不使用would have done, should have done。
第三类条件句表示想象的事情，这和第二类条件句相似。但是第三类条件句永远不可能发生，因为第三类条件句描述的是与过去相反的事情。
在第三类条件句中，had可以倒装：
Had the management acted sooner, the strike wouldn’t have happened.
如果管理层早点采取行动，罢工就不会发生了。
if I had been sb/ if I had been one’s position 用来描写站在他人立场可能会采取的行动
If I had been you, I’d have accepted their offer.
If I had been in your position, I’d have accepted their offer.
如果我是你，我早就接受他们的提议了。（你本该接受他们的建议）
if it hadn’t been for 用来接收为什么某事在过去没有发生：
If it hadn’t been for the rain, we would have had a good harvest.
如果不是因为下雨，我们本会有一个好收成。
Had it not been for the unusually bad weather, the rescue party would have been able to save the stranded climber.
如果不是因为天气异常恶劣，救援队本可以救出被困的登山者。
变体I
if+过去完成时， 情态动词（could, might, should）+have done
如果想象的结果可能性更小、或者指能力的时候，可以用以上三个情态动词代替。could表示能力，might表示更小的可能性，should表示应该。
If he had been here yesterday, he could have told us.
如果他昨天在这里，他本可以告诉我们的。
If he had received a present, he should have thanked her.
如果他收到了礼物，他应该感谢她。
If he had been here, he could have been helping us in the shop.
如果他在这里，他可能会在商店里帮助我们。
含蓄条件句
含蓄条件句指不含if，unless的条件句。
With luck (= if we are lucky) , we’ll be there by tomorrow.
如果运气好的话，我们明天就会到那里。
Given time (= if we give them time), they’ll probably agree.
如果我们给他们时间，他们可能会同意的。
To hear him talk (=if you could hear him talk), you’d think he was Prime Minister.
听他讲话，你会以为他是首相哩。
I would write to her, but I don’t know her address (=if I knew her address).
我会写信给她，但我不知道她的地址。
But for his pension (= if he didn’t have his pension), he would starve.
如果没有退休金，他就会饿死了。
Without your help ( = if you hadn’t helped), I couldn’t have done it.
如果没有你的帮助，我不可能做成这件事。
In different circumstances (= if circumstances had been different), I would have said yes. 如果情况不同，我会答应的。
if的其他含义
if表示当……时（=when）
If it rains heavily, our river floods. 每当下大雨时，我们这条河流就泛滥。
if意谓when时指永久性的真理。主句的时态可以是用will，也可以用一般现在时。
If you boil water, it turns/will turn into steam.
你把水烧开，水就变成气态。