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if 引导的条件句if引导的条件句表示在某种条件下，会导致另一事发生。
句式为if +从句，主句。
中文意思是“如果某事发生（或不发生），另一事就（不）发生”。
通常分以下两种情形：一、真实条件句1. if从句和主句都用一般现在时，表示客观真理或习惯和持续发生的事情。
如：If the moon goes near the earth, the tide goes high. 如果月亮离地球距离近，潮水就高。
2. if从句用一般现在时，主句用一般将来时，表示从句中的动作如果发生，那么主句中的动作也将发生。
如：If it stops raining later this afternoon, we will eat out. 如果今天下午晚些时候雨能停，我们就出去吃饭。
3. if从句用一般现在时，主句用祈使句，表示给某人提建议或命令某人做某事，及提出建议或请求。
如：If you are not likely to be in town, please let me know. 如果你不可能在城里，请让我知道。
二、虚拟条件句虚拟条件句，也称非真实条件句，表示在某种假想的条件下，将导致某事发生。
从句中所陈述的事情仅仅只是说话者的想法，不是事实，也不可能发生。
1. if从句用一般过去时（did / were），主句用would / could / should / might + do，表示现在不可能发生的事情，if 从句中所陈述的事情与现在的事实相反。
如：If I were Liu Xiang, I would train hard for the 2008 Olympic Games.如果我是刘翔，我会为了2008年奥运会努力训练。
2. if从句用一般过去时（did / were或 were to + do），主句用would / could / should / might + do。
表示将来不可能发生的事情，if 从句中所陈述的事情与将来的事实相反。
一、含if的真实条件句和虚拟条件句1、在英语中，语气是动词的一种形式，用来表示说话人的意图或态度。
英语的语气有三种：陈述语气（表示所说的话是事实），祈使语气（表示所说的话是请求或命令）和虚拟语气（表示所说的话只是一种主观的愿望或假设或建议等）。
如果所表示的条件是真实的，或者完全有可能实现的，叫真实条件句，主句和从句的谓语都用陈述语气。
2、在含有were, had, 或者should 等词的虚拟条件句中，可以省略if, 将were, had或者should这些助动词放在句首。
二、被动语态1. 被动语态的基本时态变化被动语态通常为十种时态的被动形式, 被动语态由be＋过去分词构成，be随时态的变化而变化。
以do为例，各种时态的被动语态形式为：1) am/is/are +done (过去分词) 一般现在时2）has /have been done 现在完成时3）am/is /are being done 现在进行时4）was/were done 一般过去时5）had been done 过去完成时6）was/were being done 过去进行时7）shall/will be done/ be going to be done/ be about to be done/ be to be to done一般将来时8）should/would be done/was\were going to be done/ was\were about to be done/was\were to be to done过去将来时9）shall/will have been done 将来完成时（少用）10）should/would have been done 过去将来完成时（少用）2. 被动语态的特殊结构形式1)带情态动词的被动结构。
其形式为：情态动词＋be＋过去分词。
2) 有些动词可以有两个宾语，在用于被动结构时，可以把主动结构中的一个宾语变为主语，另一宾语仍然保留在谓语后面。
if 条件句if条件句是一种高级的语法结构，它用来表达一个假设或者一个可能的情况。
if条件句可以用在日常交流中，也可以用在实际生活中。
下面我们来详细的讲解if条件句。
一、if条件句的基本形式if条件句的基本形式是：if + 主语 + 谓语，如：如果条件成立，则执行相应的结果。
if条件句可以分为三种类型：1、真实条件句真实条件句是指一个可能的情况，它可以发生，也有可能不发生。
真实条件句的形式是if + 现在时态，主将未来时，表示未来的可能情况，例如：If he comes, I will tell him the truth.（如果他来了，我会告诉他实话。
）2、虚拟条件句虚拟条件句是指一个虚假或虚构的情况，它不可能实现或已经过去了。
虚拟条件句的形式是if + 过去时态，过去完成时态或would + 动词原形，表示与现在相反、与过去相反或者未来不可能的情况，例如：如果我知道了，现在会有不同的结果。
非真实条件句和虚拟条件句很相似，但是它所表达的情况是存在的，只是比较困难或者需要经过一些条件才能实现。
非真实条件句的形式是如果+过去式，主语+would/could/might+动原。
例如：If I were you, I would study hard.（如果我是你，我会努力学习。
）如果我成为你的话，然后可能做的事情。
if条件句的基本引导词是if，但是我们还可以使用其他的引导词，例如：1、UnlessUnless是“除非”、“如果不”的意思，它是对if的否定形式。
例如：如果你不和我一起去，我不会执行此动作。
2、Provided thatProvided that是“只要”，“在条件下”之意，例如：Provided that the weather is fine, we will have a picnic tomorrow.（只要天气好，我们明天就去野餐。
）在此条件下，我们会执行此活动。
四、if条件句的注意事项1、if的位置主语和谓语之间要有if，如果把if放在其他位置，意思会变得模糊。
If 引导条件句的用法1、真实条件句用于陈述语气,假设的情况可能发生,其中if 是如果的意思;时态关系句型：条件从句主句一般现在时shall/will + 动词原形If he comes, he will bring his violin.典型例题The volleyball match will be put off if it ___.A. will rainB. rainsC. rainedD. is rained答案B;真实条件句主句为将来时,从句用一般现在时;注意：1 在真实条件句中,主句不能用be going to表示将来,该用shall, will.错If you leave now, you are never going to regret it.对If you leave now, you will never regret it.2 表示真理时,主句谓语动词便不用shall will +动词原形,而直接用一般现在时的动词形式;2 非真实条件句1时态：可以表示过去,现在和将来的情况;它的基本特点是时态退后;a. 同现在事实相反的假设;句型：条件从句主句一般过去时should would +动词原形If they were here, they would help you.b. 表示于过去事实相反的假设;句型：条件从句主句过去完成时shouldwould have+ 过去分词If she had worked harder, she would have succeeded.The rice would not have been burnt if you had been more careful.If my lawyer had been here last Saturday, he would have prevented me from going.If he had come yesterday, I should / would have told him about it.含义：He did not come yesterday, so I did not tell him about it.If he had not been ill and missed many classes, he would have made greater progress.含义：He was ill and missed many lessons, so he did not make greater progress.c. 表示对将来的假想句型：条件从句主句一般过去时should+ 动词原形were+ 不定式would + 动词原形should+ 动词原形If you succeeded, everything would be all right.If you should succeed, everything would be all right.If you were to succeed, everything would be all right.3 混合条件句主句与从句的动作发生在不同的时间,这时主,从句谓语动词的虚拟语气形式因时间不同而不同,这叫做混合条件句;If you had asked him yesterday, you would know what to do now.从句与过去事实相反,主句与现在事实相反;If it had rained last night 过去, it would be very cold today 现在.4 虚拟条件句的倒装虚拟条件句的从句部分如果含有were, should, 或had, 可将if省略,再把were, should或had 移到从句句首,实行倒装;Were they here now, they could help us.=If they were here now, they could help us.Had you come earlier, you would have met him=If you had come earlier, you would have met him.Should it rain, the crops would be saved.=Were it to rain, the crops would be saved.注意：在虚拟语气的从句中,动词’be’的过去时态一律用"were",不用was,即在从句中be用were代替;If I were you, I would go to look for him.如果我是你,就会去找他;If he were here, everything would be all right.如果他在这儿,一切都会好的;典型例题_____ to do the work, I should do it some other day.A. If were IB. I wereC. Were ID. Was I答案C. 在虚拟条件状语中如果有were, should, had这三个词,通常将if省略,主语提前, 变成were, should, had +主语的形式;但要注意,在虚拟条件状语从句中,省略连词的倒装形式的句首不能用动词的缩略形式;如我们可说Were I not to do., 而不能说Weren’t I to do.5 特殊的虚拟语气词：should1 It is demanded / necessary / a pity + that…结构中的主语从句的谓语动词要用should 加动词原形, should 可省略;句型：1suggestedIt is 2important that…+ should do3 a pity1suggested, ordered, proposed, required, demanded, requested, insisted；+ should do2important, necessary, natural, strangea pity, a shame, no wonder3It is suggested that we should hold a meeting next week.It is necessary that he should come to our meeting tomorrow.2在宾语从句中的应用在表示命令、建议、要求等一类动词后面的从句中;order, suggest, propose, require, demand, request, insist, command, insist + should doI suggest that we should hold a meeting next week.He insisted that he should be sent there.注意：如suggest, insist不表示"建议" 或"坚持要某人做某事时",即它们用于其本意"暗示、表明"、"坚持认为"时,宾语从句用陈述语气;The guard at gate insisted that everybody obey the rules.判断改错:错You pale face suggests that you should be ill.对Your pale face suggests that you are ill.错I insisted that you should be wrong.对I insisted that you were wrong.3在表语从句,同位语从句中的应用在suggestion, proposal, idea, plan, order, advice等名词后面的表语从句、同位语从句中要用虚拟语气,即should+动词原形;My idea is that we should get more people to attend the conference.I make a proposal that we should hold a meeting next week.。
if引导的条件句是什么从句if 引导的条件句有真实条件句和非真实条件句两种；1、真实条件句：叙述真实可能发生的事情；例句：If you fail in the exam,you will let him down.如果你考试不及格，你会让他失望的。
扩展资料2、非真实条件句：虚拟语气的一种，表示与实际已发生事实相反：例句：If I were you, I would invite him.如果我是你，我会邀请他。
3、另一个常用连词为unless,大多数时候意思与 if not 相近：例句：Let's go out for a walk unless you are too tired.我们出去散步吧，除非你太累了。
例句：If you are not too tired, let's go out for a walk.如果你不太累，我们出去散步吧。
条件状语从句的基本用法1、用if引导：if意为“如果”。
例句：If you cheat in the exam you’ll never get away with it.考试作弊必予追究。
2、用unless引导：unless的意思是“如果不”“除非”。
例句：Unless you go at once you will be late.如果你不马上走，就会迟到的'。
3、用as [so] long as引导：as [so] long as的意思是“如果”“只要”。
例句：I’ll remember that day as long as I live.只要我活着，我就不会忘记那个日子。
4、用in case引导：in case用连词引导条件状语从句时，其意为“如果”“万一”。
例句：In case I forget, please remind me about it.万一我忘记，请提醒我一下。
5、条件状语从句的时态：当主句为将来时态或含有将来意义时，条件状语从句习惯上要用一般现在时表示将来意义，而不能直接使用将来时态。
if 引导的非真实性条件状语从句即虚拟语气通过动词形式的变化来表示说话人对发生的动作或存在的状态所持的态度或看法的动词形式称为语气。
.英语中的语气分三种：陈述语气、祈使语气、虚拟语气。
虚拟语气表示说话人所说的话不是事实，而是一种祝愿，建议，与事实相反的假设或实际可能性不大的情况等（即非真实的假设）。
If 引导的条件状语从句分为真实和非真实条件句（虚拟条件句）。
真实条件句表示在假设的条件下，有可能实现的情况。
非真实条件句表示的是假设的或实际可能性不大的情况，故采用虚拟语气。
If he doesn’t hurry up, he will miss the bus.( 真实条件状语)If he was free, he asked me to tell stories.（真实条件状语）If I were you, I would go at once.（非真实条件状语从句）If there was no air, people would die.（非真实条件状语从句）1）非真实条件句中虚拟语气的基本形式。
假设类型条件从句的动词结果主句的动词与现在事实相反动词过去式（be只用were）would/should/could/might + 动词原形与过去事实相反 had+过去分词 would/should/could/might +have + 过去分词与将来事实相反动词过去式/(should/were to)+动词原形would/should/could/might + 动词原形①与现在事实相反If I had time, I would go for a walk.如果我有时间，我就会去散步。
(实际情况：我现在没有时间，也不会去散步。
)If I were you, I would take an umbrella.假如我是你的话，我会带上雨伞。
(事实上我不可能是你。
)I would say no if someone asked me to be in a movie.假如有人请我当电影演员，我会表示拒绝。
条件句有真实条件句与非真实条件句两种
●真实条件句（第一类条件句）所表的假设是可能发生或实现的，句中的条件从句与结果主句皆用直陈语气。
●非真实条件句所表的假设则是不可能或不太可能发生或实现的，句中的条件从句与结果主句皆须用虚拟语气。
1.与现在事实相反（第二类条件句）条件从句用If +动词过去式（be的过去式用were），
结果主句用should/would+动词原形。
谈论想像中的情况或描写完全不可能的事。
2.与将来事实相反（第二类条件句）条件从句If+动词过去式（be的过去式用were）结果
主句用should/would+动词原形。
第二类的形式与第一类不同，If从句中用一般过去时，谈论想像的情况，主句用would+动词原形，推测想像的结果。
尽管第二类使用过去时，却并非指过去的时间，所以，If之后的过去时用法常被称为“非真实的过去”
3.与过去事实相反（第三类条件句称为“假设条件句”），条件从句If +had+过去分词，结
果主句用should/ would +have+过去分词。
第三类条件句在If从句里设想纯粹想像的事情，在主句里讲述想像的结果。
它与第二类条件句有一定的相似之处。
但是，第三类所谈论的是没有或永远不可能有的结果。
因为它们指的是去没有过的事情。
（在If从句中可用could have+过去分词代替，或had been able to+动词原形）。
if引导的非真实性条件状语从句即虚拟语气（最新整理）if 引导的非真实性条件状语从句即虚拟语气通过动词形式的变化来表示说话人对发生的动作或存在的状态所持的态度或看法的动词形式称为语气。
.英语中的语气分三种：陈述语气、祈使语气、虚拟语气。
虚拟语气表示说话人所说的话不是事实，而是一种祝愿，建议，与事实相反的假设或实际可能性不大的情况等（即非真实的假设）。
If 引导的条件状语从句分为真实和非真实条件句（虚拟条件句）。
真实条件句表示在假设的条件下，有可能实现的情况。
非真实条件句表示的是假设的或实际可能性不大的情况，故采用虚拟语气。
If he doesn’t hurry up, he will miss the bus.( 真实条件状语)If he was free, he asked me to tell stories.（真实条件状语）If I were you, I would go at once.（非真实条件状语从句）If there was no air, people would die.（非真实条件状语从句）1）非真实条件句中虚拟语气的基本形式。
假设类型条件从句的动词结果主句的动词与现在事实相反动词过去式（be只用were）would/should/could/might + 动词原形与过去事实相反had+过去分词would/should/could/might + have + 过去分词与将来事实相反动词过去式/(should/were to)+动词原形would/should/could/might + 动词原形①与现在事实相反If I had time, I would go for a walk.如果我有时间，我就会去散步。
(实际情况：我现在没有时间，也不会去散步。
)If I were you, I would take an umbrella.假如我是你的话，我会带上雨伞。
(事实上我不可能是你。
Li's question:if条件状语从句中，是不是只要主句不用一般将来时，从句可以用任何时态？CC's answer:if 的条件从句分为真实条件从句和非真实条件句（虚拟条件从句）。
真实条件从句：是假设有可能发生的。
在新概念一册第137课里：If I win a lot of money I'll buy you a mink coat. …… If we win a lot of money we'll travel round he world.……就是经典的“主将从现”（主句将来时，从句一般现在时）。
在新概念二册第16课里回顾了一册的真实条件句：If you park your car in the wrong place, a traffic policeman will soon find it.……If you receive a request like this, you cannot fail to obey it!非真实条件句（虚拟条件从句）:是假设不太可能发生的。
在新概念英语第二册第40课，也就是第二单元的第16课（亚历山大先生真是太有才啦），文中出现的是非真实条件句的与现在事实相反的假设和对不可能发生情况的假设：If you ate more and talked less, we would both enjoy our dinner! 句中的 ate more and talked less 还令我联想到了一册第109课：Eat more and smoke less! That's very good advice! （新概念就是这样温故而知新，层次分明，逐步加深，堪称英语学习的宝典）；在第64课（第三单元的第16课）出现的是非真实条件句的与过去事实相反的假设：The tunnel would be well-ventilated if tall chimneys were built above sea level.最后对if条件句的总结在第88课（第四单元的第16课）：If they are not brought to the surface soon they may lose their lives.……If explosives are used, vibrations will cause the roof of the mine to collapse,……If they had not been a hard layer of rock beneath the soil, they would have completed the job in a few hours.……If they knew how difficult it was to drill through the hard rock, they would lose heart.if的虚拟语气有三种：1.与现在事实相反:从句动词过去式，主句用would/could/should/might+动词原形e.g. If I were you, I would ask him his telephone number.2.与过去事实相反：从句had+动词过去分词，主句would/could/should/might+have+动词过去分词e.g. If I had know that yesterday, I would have told you.3. 与将来事实相反：从句should/were to + 动词原形，主句would/could/should/might+动词原形e.g. If it should rain, the crops might be saved.。
