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条件状语从句语法讲解

由引导词if或unless引导的状语从句叫做条件状语从句。在英文中，条件是指某一件事情实现之后（状语从句中的动作），其它事情（主句中的动作）才能发生，通常译作“假如”。（注意：在含有条件状语从句的复合句中，表示将来时态，主句是一般将来时态。如有祈使句或情态动词，从句要用现在时态,[主将从现原则]（主将从现，将并非指将来时，还指表示将来含义的，跟着if后的那句话是从句。）语法引导条件状语从句最常用的连词是if,由if引导的条件状语从句表示在某种条件下某事很可能发生。如：1） If you ask him,he will help you.

如果你请他帮忙，他会帮你的。

2） 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

if引导的条件状语从句既可以将从句放前面也可以将从句放后面（如果天下雨，我们就不玩了）If it rains,we will stop playing.‘转为We will stop playing if it rains.

if引导的条件状语从句

另外，if从句还表示不可实现的条件或根本不可能存在的条件，也就是一种虚拟的条件或假设，从句多用一般过去时或过去完成时。如：If I were you,I would invite him to the party.如果我是你，我

会邀请他参加聚会。I would have arrived much earlier if I had not been caught in the traffic.如果没有堵车，我会到的早一点儿。那么，除了if之外，是否还有其他连词也可以引导条件状语从句呢?回答是肯定的，不仅有，还有很多。这些词由于出现的频率较小，且用法较复杂一些，所以不如if为大家所熟知罢了。下面就这些词的用法以例句的形式进行一下简单总结: 1、unless conj.除非，若不，除非在……的时候

You will fail to arrive there in time unless you start earlier.如果你不早点动身，你就不能及时赶到那儿。

Unless it rains,the game will be played.除非下雨，比赛将照常进行。

2、on condition(that)...在……条件下，如果 on condition (that)...引导的条件从句是主句事件发生的前提条件或唯一条件。

I can tell you the truth on condition that you promise to keep a secret.我可以告诉你真相，条件是你答应保密。

You can go swimming on condition (that) you don't go too far from the river bank.你只有在不远离河岸的条件下才可以下水游泳。

3、supposing conj.如果，假如 supposing引导的条件从句表示一种假设条件。

Supposing it rains,shall we continue the sports meeting?倘若下雨，我们的运动会还要继续举行吗?

Supposing anything should go wrong,what would you do then?假如出了什么问题，你准备怎么对付?

4、provided conj.假如，除非，以……为条件 provided (that) +从句表示一种假设条件。

He will sign the contract provided we offer more favorable terms.如果我们提出更优惠的条件，他就会在合同上签字。

He won't be against us in the meeting provided that we ask for his advice in advance.如果我们提前征求一下他的意见，他就不会在会上反对我们。

从上述例句可以看出if,unless,on condition (that),supposing,provided等词引导的条件状语从句，主从句条件关系分明，结构清晰。但有些句子，虽没有含条件关系的连词，却也隐含着条件关系，这些句子常用一些词，如but for,without等引出一个介词结构来表示条件，条件应该是虚拟的，或与事实相反的假设。如：but for若非，要不是But for the rain,we should have a pleasant journey.

要不是下雨，我们的旅行肯定会很愉快。

But for your help,we should not have finished in time.

要不是你帮忙，我们肯定不能及时完成任务

经典语句：If it dosen't rain tomorrow,we will go to the zoo.If you open the door，i will come in.条件状语从句就是用以表示“在某种条件下，会……”常用if,in case,on condition等词来引导连

接词主要有if,unless,as/so long as,on condition that,provided,suppose,supposing 等..主句用一般将来时，if或

【注：在条件状语从句中，unless引导的条件状语从句用一般现在时。

绝大数情况下some要变为any。】条件状语用法编辑unless = if...not

e.g. Let's go out for a walk unless you are too tired. If you are not too tired,let's go out for a walk.if 引导的条件句有真实条件句和非真实条件句两种：真实条件句如：If it rains tomorrow,we won’t go on a park非真实条件句是虚拟语气的一种，表示与事实相反，如：If I were you,I would go with him.so/as long as只要由as (so) long as,in case引导。So long as you’re happy,it doesn’t matter what you do.

只要你高兴，你做什么都没有关系。

You may borrow my book as long as you keep it clean.

只要你保持书的清洁，你就可以把我的书借去。

Take your umbrella in case it rains.

带着你的伞吧，以防下雨。

例句引导条件状语从句的连词有：if（如果），unless（除非；如果不），as long as（除非；只要），supposing（假设），on condition that（条件是），in case（如果）。【例】You can't learn English well unless you work hard.

除非你努力学习，否则你学不好英语。

You can use my bike on condition that you return it by Friday.

你可以使用我的自行车，条件是你星期五以前还。

1）学习条件状语从句应注意以下几点：⑴条件状语从句中一般不使用将来时态，尽管主句使用将来时态，而从句用一般现在时或现在完成时。【例】I will come to see you if I have time.

我有时间，我就来看你。

If the rain stops,I shall go out for a walk.

如果雨停了，我就出去散步。

⑵注意条件状语从句在虚拟语气中的使用。【例】If I were to I should first of all get the experts to discuss the plan.

如果我真的想做这事，我首先会找专家们讨论我的计划。

⑶条件状语从句中的省略。【例】Come tomorrow if possible. 可能的话，明天来。I will buy a DVD set if necessary.

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