状语从句是在复合句中修饰主句中的动词、形容词、副词或者整个主句的句子。状语从句由从属连词引导,从属连词在状语从句中不充当句子成分。状语从句可分为时间、原因、条件、目的、结果、比较、方式、地点状语从句和让步状语从句。
(1)由从属连词when引导的时间状语从句。When意为“当……的时侯”,when既可以表示一段时间,一个持续性的动作,也可以表示时间的一个点,一个短暂性的动作。主、从句的动作可以同时发生,从句的动作也可发生在主句之前或之后。例如:
Tom went to work in the factory when he was 14 years old.
Mr Brown had already left when I got to his office.
(2)由until引导的时间状语从句。until/till意为“直到……”,主句的谓语动词必须是持续性动词,而且主从句的谓语动词都用肯定式。“not...until...”表示“直到……才……”时,主句的谓语动词必须是非持续性动词,而且主句用否定式,从句用肯定式。例如:
I didn't go to bed until my granny came back home.
Let's wait until tomorrow.
(3)由as soon as和since引导的时间状语从句。as soon as意为“一……就……”,一般主句的谓语动词用将来时时,从句的谓语动词用现在时。since意为“自从……以来”,通常从句的谓语动词用一般过去时,而主句的谓语动词用现在完成时。例如:
I'll let you know as soon as he comes back.
Mr Read has taught in that school since he left Canada in 1988.
(4)由从属连词if引导的条件状语从句,主句用一般将来时,从句要用一般现在时表示将来时间。例如:
We'll have a sports meeting if it doesn't rain tomorrow.
(5)由because,as,since引导的原因状语从句。because的语气最强烈,通常用来回答why提出的问句。because引导的原因状语从句经常放在主句之后;since的语气比because弱,陈述的理由往往是对方所知道的,译作“既然”;as的语气最弱,只是附带较明显的原因或理由,as引导的从句常放在主句之前,说明原因或理由,后面的主句说明结果,主从句所表达的内容同等重要。例如:
As it was dark,we stopped working.
Since no one is against it,we'll do that.
Betty didn't go to see the film yesterday because she was ill.
(6)比较状语从句由than,as...as,not as(so)...as来引导,从句中往往省去与主句相同的成分。例如:My brother is younger than I.He worked as fast as an old worker.
(7)表示结果:so that,so...that,such...that.其中so是副词,后接副词或形容词,such是形容词,后接名词或名词短语。例如:
The old man was so weak that he couldn't get on the train.
It's such an important match that we can't miss it.
(8)让步状语从句由though,although引导
though表示“尽管”,“虽然”,引导让步状语从句,可以放在主句前或主句后。注意用though就不能用but,用but就不能再用 though。例如:
This TV set is too dear though it gives you a better picture.
这句可以改为:It gives you a better picture,but this TV is too dear.
又如:He is rich,but he isn't happy.
Though he is very young,he knows several languages.
(9)表示目的的状语从句:so that。例如:
He borrowed the money so that he could send his son to school.