在复合句中作状语,其位置可以在主句前或主句后。状语从句可以分为时间、地点、原因、目的、结果、比较、让步、条件等几种。状语从句由从属连接词引导。
时间状语从句通常由when ,as ,while, after, before, since, as soon as ,since, till (until), while, whenever 等引导。时间状语从句一般放在句首或句尾,特别注意,时间状语从句不允许使用将来时,而应该用现在时替代。如: When you finish the work, you may go out to play with Sam. (你完成工作就可以出去和Jim一起玩了。) / I won’t leave until Mum comes back. (妈妈回来了我才会走。)
地点状语从句通常由 where, wherever等引导。如:Go back where you came from! (哪里来还滚到哪里去!) / I will never forget to catch the thief who stole my necklace wherever he may be. (我永远也不会忘记去抓住那个偷我项链的贼,无论他会在哪里。)
原因状语从句通常由because, since, as等引导,一般放在句首或句尾。如:He went abroad because his father had found a good university for him. (他出国了,因为他父亲给他找了一所好大学。)
目的状语从句通常由so that..., so...hat..., in order that... 等引导,往往放在句尾,从句中通常含有can / could / may / might等情态动词。如:He got up earlier so that he could catch the first train. (他起身更早为的是赶上第一班车。)
结果状语从句通常由 so that..., so...that... 等引导,放在句尾。结果状语从句一般表示已经发生的事情,故多为过去时态。如:He lost so many bikes that he decided never to buy a new one. (他丢了那么多辆自行车,他决定再也不买新车了。)
比较状语从句通常由as, than, as (so)...as等引导,一般省略从句的谓语部分,只剩下名词或代词(用主格或宾格均可)。如:Jane is much taller than I/me. (Jane比我高多了。) / I don’t have as many books as you (do). (我书没有你多)
让步状语从句通常由though (although), as, even if( even though), however, whatever等引导。如:Even if you pay the debt(债务) for me, I will not thank you because it has nothing to do with me. (即使你替我还了债我也不会感谢你,因为它与我毫无关系。) / He wears a T-shirt though it is very cold. (他穿了一件T恤衫,尽管天很冷。)
条件状语从句通常由if, unless, as long as等引导,条件状语从句一般放在句首或句尾,特别注意,时间状语从句不允许使用将来时,而应该用现在时替代。You will certainly fail in the coming final exams unless you work much harder. (即将来到的期末考试你肯定考不及格,除非你更用功。) / If it doesn’ t rain tomorrow, we shall go hiking. (如果明天不下雨我们就要去徒步旅行。)
[注意]
1、because与so;(al)though与but;if与so不可以同在一个句子中成对出现。
2、时间、条件、原因,让步状语从句放在句首时需要用逗号与主句隔开。