状语从句的概念：

状语从句指句子用作状语时，起副词作用的句子。它可以修饰谓语、非谓语动词、定语、状语或整个句子。根据其作用可分为时间、地点、原因、条件、目的、结果、让步、方式和比较等从句。状语从句一般由连词(从属连词)引导，也可以由词组引起。从句位于句首或句中时通常用逗号与主句隔开，位于句尾时可以不用逗号隔开。

1、地点状语从句
   地点状语从句通常由where, wherever 引导。
   Where I live there are plenty of trees.
   我住的地方树很多。
   Wherever I am I will be thinking of you.
   不管我在哪里我都会想到你。
2、方式状语从句
   方式状语从句通常由as, (just) as…so…, as if, as though引导。
1）as, (just) as…so…引导的方式状语从句通常位于主句后，但在(just) as…so…结构中位
   于句首，这时as从句带有比喻的含义，意思是“正如…”，“就像”，多用于正式文体，例如：
   Always do to the others as you would be done by.
   你希望人家怎样待你，你就要怎样待人。
   As water is to fish, so air is to man.
   我们离不开空气，犹如鱼儿离不开水。
   Just as we sweep our rooms, so we should sweep backward ideas from our minds.
   正如打扫房屋一样，我们也要扫除我们头脑中落后的东西。
2）as if, as though
   两者的意义和用法相同，引出的状语从句谓语多用虚拟语气，表示与事实相反，有时也用陈述语气，
   表示所说情况是事实或实现的可能性较大。汉译常作“仿佛……似的”，“好像……似的”，例如：
   They completely ignore these facts as if (as though) they never existed.
　 他们完全忽略了这些事实，就仿佛它不存在似的。（与事实相反，谓语用虚拟语气。）
　 He looks as if (as though) he had been hit by lighting.
　 他那样子就像被雷击了似的。（与事实相反，谓语用虚拟语气。）
   It looks as if the weather may pick up very soon.
   看来天气很快就会好起来。（实现的可能性较大，谓语用陈述语气。）
   说明：as if / as though也可以引导一个分词短语、不定式短语或无动词短语，例如：
   He stared at me as if seeing me for first time.
   他目不转睛地看着我，就像第一次看见我似的。
   He cleared his throat as if to say something.
   他清了清嗓子，像要说什么似的。
   The waves dashed on the rocks as if in anger.
   波涛冲击着岩石，好像很愤怒。
3、原因状语从句
   比较：because, since, as和for
1）because语势最强，用来说明人所不知的原因，回答why提出的问题。当原因是显而易见的或已
   为人们所知，就用as或 since。
　 I didn't go, because I was afraid.
　 Since /As the weather is so bad, we have to delay our journey.
2）由because引导的从句如果放在句末，且前面有逗 号，则可以用for来代替。但如果不是说明直
   接原因， 而是多种情况加以推断，就只能用for。
　 He is absent today, because / for he is ill.
　 He must be ill, for he is absent today.
4、目的状语从句
   表示目的状语的从句可以由that, so that, in order that, lest, for fear that, in case
   等词引导，例如：
　 You must speak louder so that /in order that you can be heard by all.
　 He wrote the name down for fear that(lest) he should forget it.
　 Better take more clothes in case the weather is cold.
5、结果状语从句
   结果状语从句常由so… that 或 such…that引导，掌握这两个句型，首先要了解so 和 such
   与其后的词 的搭配规律。
比较：so和 such
其规律由so与such的不同词性决定。such 是形容词，修饰名词或名词词组，so 是副词，只能修饰
形容词或副词。 so 还可与表示数量的形容词many, few, much, little连用，形成固定搭配。
   so foolish　　　　　　　such a fool　　　　　　　
   so nice a flower　　　　such a nice flower　 　　
   so many / few flowers　 such nice flowers　　　　
   so much / little money. such rapid progress　　　
   so many people　　　　　such a lot of people　 　
（so many 已成固定搭配，a lot of 虽相当于 many，但 a lot of 为名词性的，只能用such搭配。）
   so…that与such…that之间的转换即为 so与such之间的转换。
   The boy is so young that he can't go to school.
   He is such a young boy that he can't go to school
6、条件状语从句
   连接词主要有 if, unless, as/so long as, on condition that 等。.
   if 引导的条件句有真实条件句和非真实条件句两种。非真实条件句已在虚拟语气中阐述。
   unless = if not.　
   Let's go out for a walk unless you are too tired.
   If you are not too tied, let's go out for a walk.
典型例题
   You will be late ___ you leave immediately.　
   A. unless　 B. until　 C. if　　D. or
   答案：A。 句意：除非你立即走，否则你就回迟到的。可转化为 If you dong leave immediately, 
             you will be late.　B、D句意不对，or表转折，句子如为 You leave immediately or
             you will be late.
7、让步状语从句
   though, although
　 注意： 当有though, although时，后面的从句不能有but，但是 though 和yet可连用
　 Although it's raining, they are still working in the field.　
　 虽然在下雨，但他们仍在地里干活。
　 He is very old, but he still works very hard.　
　 虽然他很老，但仍然努力地工作。
　 Though the sore be healed, yet a scar may remain.
　 伤口虽愈合，但伤疤留下了。 （谚语）
   典型例题
1）___ she is young, she knows quite a lot.　
   A. When　B. However　 C. Although　 D. Unless
   答案：C。意为虽然她很年轻，却知道许多。
2）as, though 引导的倒装句
　 as / though引导的让步从句必须表语或状语提前（形容词、副词、分词、实义动词提前）。
　 Child as /though he was, he knew what was the right thing to do.
　 = Though he was a small child, he knew what was the right thing to do.
   注意：a. 句首名词不能带任何冠词。
　　　   b. 句首是实义动词，其他助动词放在主语后。如果实义动词有宾语和状语，随实义动词
            一起放在主语之前。
   Try hard as he will, he never seems able to do the work satisfactorily.
   = Though he tries hard, he never seems…
   虽然他尽了努力，但他的工作总做的不尽人意。
3）ever if, even though.　即使
　 We'll make a trip even though the weather is bad.
4）whether…or　 不管……都
　 Whether you believe it or not
5）"no matter +疑问词" 或"疑问词+后缀ever"
　 No matter what happened, he would not mind.
　 Whatever happened, he would not mind.
　 替换：no matter what = whatever
         no matter who = whoever
　　　　 no matter when = whenever
　　　　 no matter where = wherever
　　　　 no matter which = whichever
         no matter how = however
　 注意：no matter 不能引导主语从句和宾语从句。
　（错）No matter what you say is of no use now.
　（对）Whatever you say is of no use now.
　　　 你现在说什么也没用了。(Whatever you say是主语从句)
　（错）Prisoners have to eat no matter what they're given,
　（对）Prisoners have to eat whatever they're given.　囚犯们只能给什么吃什么。
8、比较while, when, as
1）as, when 引导短暂性动作的动词。
　 Just as / Just when / When I stopped my car, a man came up to me.
2）当从句的动作发生于主句动作之前，只能用when 引导这个从句，不可用as 或 while。
　 When you have finished your work, you may have a rest.
3）从句表示"随时间推移"连词能用as，不用when 或while。
　 As the day went on, the weather got worse.　
　 日子一天天过去，天气越变越坏。
9、比较until和till
   此两个连词意义相同。肯定形式表示的意思是"做某事直至某时"，动词必须是延续性的。否定
   形式表达的意思是"直至某时才做某事"。动词为延续性或非延续性都可　以。 正确使用这两
   个连词的关键之一就在于判断句中的动词该用肯定式还是否定式。
肯定句：
   I slept until midnight. 我一直睡到半夜时醒了。
   Wait till I call you.　 等着我叫你。
（在肯定句中可用before代替 Let's get in the wheat before the sun sets.）
否定句：
   She didn't arrive until 6 o'clock.
   她直到6点才到。
   Don't get off the bus until it has stopped.
   公共汽车停稳后再下车。
   I didn't manage to do it until you had explained how.　 直到你教我后，我才会做。
10、表示"一…就…"的结构
   hardly/scarcely…when/before, no sooner…than　和as soon as都可以表示"一…就…"的意思，例：
   I had hardly / scarcely got home when it began to rain.
   I had no sooner got home than it began to rain.
   As soon as I got home, it began to rain.
   注意：如果hardly, scarcely 或no sooner置于句首，句子必须用倒装结构：
　       Hardly / Scarcely had I got home when it began to rain.
　       No sooner had I got home than it began to rain

状语从句的用种类：

1、时间状语从句：
表示时间的状语从句可由when, as, while, whenever, after, before, till(until), since, once, as soon as(或the moment), by the time, no sooner…than, hardly(scarcely)… when, everytime等引导。 　　
e.g. When I came into the office, the teachers were having a meeting. 　　
       He started as soon as he received the news. 　　
       Once you see him, you will never forget him. 　　
       No sooner had I gone to bed than I went to sleep. 　　
2、原因状语从句：
原因状语从句是表示原因或理由的，引导这类从句的最常用的连词是because, since, as, nowthat（既然）等，for表示因果关系时（它引导的不是从句）为并列连词，语气不如because强。 　　e.g. He is disappointed because he didn't get the position. 　　
      As it is raining, I will not go out. 　　
      Now that you mention it, I do remember. 　　
3、地点状语从句： 　　
引导地点状语从句的连词是where和wherever等。 　　
e.g. Sit wherever you like. 　　
      Make a mark where you have a question. 　　
4、目的状语从句： 　　
引导目的状语从句最常用的词（组）是so, so that（从句谓语常有情态动词）, in order that, in case（以防，以免）等。 　　
e.g. Speak clearly, so that they may understand you. 　　
      She has bought the book in order that she could follow the TV lessons. 　　
      He left early in case he should miss the train. 　　
5、结果状语从句： 　　
结果状语从句是表示事态结果的从句，通常主句是原因，从句是结果。由so that（从句谓语一般没有情态动词）,so…that, such…that等引导。 　　
e.g. She was ill, so that she didn't attend the meeting. 　　
      He was so excited that he could not say a word. 　　
      She is such a good teacher that everyone admires her. 　　
6、条件状语从句： 　　
条件状语从句分真实性（有可能实现的事情）与非真实性（条件与事实相反或者在说话者看来不大可能实现的事情）条件句。
引导条件状语从句的词（组）主要有if, unless, so(as)long as, on condition that, so(as) far as, if only(=if)。
注意：条件从句中的if不能用whether替换。 　　
e.g. If he is not in the office, he must be out for lunch. 　　
      You may borrow the book so long as you keep it clean. 　　
      So far as I know（据我所知）, he will be away for three months. 　　
      You can go swimming on condition that(=if) you don't go too far away from the river bank. 　　
      If he had come a few minutes earlier, he could have seen her. 　
7、让步状语从句： 　　
让步状语从句可由although, though, as, even if(though), however, whatever, whether…or, no matter who(when, what,…)等引导。
注意：as引导的让步状语从句一般是倒装的。 　　
e.g. Though he is a child, he knows a lot. 　　
      Child a she is, he knows a lot. 　　
      Whatever(=No matter what) you say, I'll never change my mind. 　　
8、方式状语从句： 　　
方式状语从句常由as, as if(though), the way, rather than等引导。 　　
e.g.You must do the exercise as I show you. 　　
      He acted as if nothing had happened. 　　
9、比较状语从句： 　　
比较状语从句常用than, so(as)…as, the more…the more等引导。 　　
e.g. I have made a lot more mistakes than you have. 　　
      He smokes cigarettes as expensive as he can afford. 　　
      The busier he is, the happier he feels.

使用状语从句时要注意的几个问题：　　

1、在时间和条件（有时也在方式、让步等）从句中，主句是一般将来时，从句通常用一般现在时表示将来。　　
e.g. We'll go outing if it doesn't rain tomorrow. 　　
       I'll write to you as soon as I get to Shanghai. 　　
2、有些时间、地点、条件、方式或让步从句，如果从句的主语与主句主语一致（或虽不一致，是it），从句的谓语又包含动词be，就可省略从句中的“主语+be”部分。　　
e.g. When(hewas) still a boy of ten, he had to work day and night. 　　
       If(you are) asked you may come in. 　　
       If(it is) necessary I'll explain to you again. 　　
3、注意区分不同从句：引导的是什么从句，不仅要根据连词，还要根据句子结构和句意来判别。以where为例，能引导多种从句。　　
e.g. You are to find it where you left it.（地点状语从句）　　
       Tell me the address where he lives.（定语从句，句中有先行词）　　
       I don't know where he came from.（宾语从句）　　
      Where he has gone is not known yet.（主语从句）　　
       This place is where they once hid.（表语从句）
注意：表示“一…就…”的结构 hardly/scarcely…when/before/no sooner…than和as soon as都可以表示“一…就…”的意思。
例句：I had hardly/scarcely got home when it began to rain.
            I had no sooner got home than it began to rain.
           As soon as I got home, it began to rain.
注意：如果hardly/scarcely或nosooner置于句首，句子必须用倒装结构：
例句：Hardly/Scarcely had I got home when it began to rain.
            No sooner had I got home than it began to rain.

1、掌握各种状语从句的含义极其运用。
2、注意状语从句中的时态运用。