4. 状语从句
（1） 定义。
起状语作用的主谓结构就是状语从句，可修饰主句中的动词、形容词和副词等。状语从句由从属连词引导。从属连词除了起连接主句和从句的作用外，它本身的词义体现主从句间的逻辑关系，所以不能省略。
（2） 位置。
状语从句必须紧跟在从属连词之后，其位置比较灵活，可在主句之前或之后，甚至可在主句句中，但要用逗号与主句隔开。如下面同样的状语从句位置就有三种。
例1. The little boys from countryside are very interested in the computer since they have never seen any of them before.
例2. Since they have never seen any of them before，the little boys from countryside are very interested in the computer.
例3. The little boys from countryside，since they have never seen any of them before，are very interested in the computer．
（3） 引导词。
引导状语从句的一般是从属连词，但有时也可能由一个起从属连同作用的词组引导。如：now that，as soon as，in case等。
（4） 分类。
根据状语从句的含义，可分为时间、地点、原因、目的、结果、方式、让步和条件八种状语从句。
1）时间状语从句可以由when（当……时），whenever（任何时候），as（当，一边……一边），while（当……的时候），before（在……之前） after（在……之后），till，until（直到），since，ever since（自从），as soon as（一……就……），now that（一……就……），once（一旦），instantly（一……就）等。例如：
例1. When I saw her，she was watching closely at the photo on the wall.
例2. Whenever there was a football match，Aioli，being a football fan，would surely go and watch.
例3. While he stood there，he heard what they were talking about.
例4. Before he came to China，the American had studied Chinese for several years．
例5. After we finished a day of hard work，the boss planned to have a party to let us take it easy.
例6. Let’s wait until the rain stops if there is enough time.
例7. Not until he came，did we begin the experiment.
例8. I haven’t seen her since she left for the U. S. A..
例9. I called him as soon as I got the latest information.
例10. Scarcely had the film started when they came．
例11. No sooner had the meeting started than they came.
例12. Every time he went to Beijing，he was used to visiting the Great Wall．
例13. Storming applause broke forth the moment he appeared on the stage．
例14. Once you understand this，you will surely make rapid progress in your study.
2）地点状语从句由where或wherever引导。例如：
例1. Wherever you are，you should follow the laws and customs there.
例2. I think the teacher will start where he stopped last time．
3）原因状语从句。
①表示原因的状语从句可以由 because，as，since，now that，seeing（that）considering that，in that等引导。例如：
例1. I think Wei Fang should be able to pass the examination because she works hard and she is clever too.
例2. Since the weather has been improved，we can go now．
例3. As he was already late，we had to go without him．
例4. The days are long for it is now July.
例5. Now that you are all here let’s discuss the possibility of building a new library.
例6. Considering that they revealed their unwillingness to help，we needn’t say anything more.
例7. Seeing（that）they are busy with their homework，we don’t need to ask them to play football.
例8. A preposition differs from a conjunction in that it introduces a phrase while the latter introduces a clause.
②也有人将be＋形容词＋that从句（that可省略）这一结构归入状语从句，本书将其归入了宾语从句，即that从句做形容词的宾语从句，但是它有表示原因的作用，that可省，但单个that不能体现逻辑关系，只有从从句的意思上理解出来。例如：
I am glad that all of you have arrived at the place on time． 大家按时到这个地方，我感到很高兴。
4）结果状语从句一般由 so that或that引导，也可见于so（such）...that句型中。例如：
例1. The wind was so fierce that we could not continue the journey and stopped.
例2. The boy left in such a hurry that he forgot to take his train ticket.
例3. He didn’t plan well，so that he didn’t finish the work as request.
在这里应特别注意so和 such在结果引导状语从句上的区别。
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 + adj. such + a（n） + n.
so + adj. + a（n） + n. such + n. （pl.）
so + adj. + n.（pl.） such +n.（pl.）
so + adj. + n.［不可数］ such +n.［不可数］
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。
5）目的状语从句。目的状语从句一般由that（以便），so that（以便），in order that（以便），lest（以免），for fear that（以免），in case（以防）等引导。例如：
例1. Give me your telephone number in case I need your help.
例2. Helen listened carefully in order that she might discover exactly what John wanted．
6）方式（或比较）状语从句（主要修饰形容词或副词）。一般由 as（正如），than（比），as ...as （和……一样），not so...as（和……不一样），as though，as if（好像）等引导。这种从句由于一些成分往往可以省略，应多加注意。
①as，as...as，than引出的方式状语从句。例如：
例1. You may do as you please.
例2. The young worker worked as fast as a skilled worker did.
例3. It is said that football is much more exciting than basketball is．
②其他。例如：
例1. At that time I couldn’t move my legs，as if they had been filled with lead．
例2. The more we can do for the people，the happier we will be.
7）让步状语从句。由though（虽然），although（虽然），as（尽管），even让（即使），even though（即使），no matte...（不管），however（无论如何），whatever（不论什么）来引导。例如：
例1. Though my father was angry，he listened to me patiently.
例2. The workers will try to finish the task in time although they were short of manpower.
例3. Patient as she was，she had no intention to listen to your complaining for three hours.
例4. However much advice you give him，they will fall deaf ears.
例5. While I admit his good points，I can see his shortcomings.
8）条件状语从句。条件状语从句可由 if（假如），unless（除非，若不），suppose（假设），supposing（假设，仅用于问句），provided（假如），as（so）long as（只要）等引导。例如：
例1. You can borrow this book as long as you keep it well.
例2. If you heat the ice，it will be melted.
例3. You can get the job on condition that you have Master’s degree.
