原因状语从句原因状语从句表原因，引导原因状语从句的从属连词主要的有because, as, since, for ，seeing (that), now (that), considering (that) ，in that 等。

以下逐一介绍常见的原因状语从句的引导词：because 引导的原因状语从句一般放于主句之后，because 表示直接原因，语气最强，最适合回答why 引导的疑问句。

例如：I do it because I like it. 我做这件事是因为我喜欢。

注意："not ... because"结构中的not否定的是because引导的整个从句，例如：The countryis not strong because it is large. 国强不在大。

since 引导的原因状语从句一般放于主句之前表示已知的、显然的理由(通常被翻译成“既然” )，较为正式，语气比because 弱。

例如：Since you are free today, you had better help me with my mathematics. 既然今天你休息，你最好帮我补习数学。

注意：seei ng (that), now (that) , con sideri ng (that) , in that 这几个词汇与si nee 引导的原因状语从句意思相近，都表示“既然” 。

例如：Seeing (that) he refused to help us, there ' s no reason that we should now help him. 他既然曾经拒绝帮助我们，我们现在没有理由要来帮助他。

Now (that) you are grown up, you should not rely on your parents. 既然你长大了，就不应该依靠你的父母了。

Considering (that) everybody is here, let 's begin our discussion. 既然大家都到了，我们就开始讨论吧。

In that he is ill, he feels unable to do it. 因为有病，他觉得做不了那件事。

as引导原因状语从句时表示附带说明的“双方已知的原因”，语气比since弱，较为正式，位置较为灵活(常放于主句之前)。

例如：As it is raining, you ' d better take a taxi. 既然在下雨，你最好乘出租汽车。

As you are tired, you had better rest. 既然累了，你最好休息一下。

I went to bed early, as I was exhausted. 我睡得早，因为我筋疲力尽了。

for 引导的原因状语从句并不说明主句行为发生的直接原因，只提供一些辅助性的补充说明，for 引导的原因状语从句只能放于主句之后并且必须用逗号将其与主句隔开。

例如：He could not have seen me, for I was not there. 他不可能见过我，因为我不在那里。

比较：because, since, as 禾口forbecause语势最强，表示不知道的原因用because，即说话人认为听话人不知道。

因此because从句是全句最重要的部分，通常被放置于主语之后。

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.for虽然表示不知道的原因，但因语气比because弱得多，是可说可不说的话，只能位于主语之后，这时，for 是并列连词，如果不是因果关系，而是对前面主语内容加以解释或推断时，只能用for。

He is abse nt today, because / for he is ill.He must be ill, for he is abse nt today.注1:除以上提到的大家比较熟悉的引导原因状语从句的从属连词外，when有时也可引导原因状语从句（when表示"既然”）I won ' t tell you when you won ' t listen.既然你不想听，我就不告诉你了。

注2: because习惯上不与so连用汉语习惯上说“因为…所以…”，但英语习惯上却不能将so与because连用：因为下雨，所以我们呆在家里。

正: Because it was raining, we stayed at home. / It was raining, so we stayed at home.误：Because it was raining, so we stayed at home.注3：because从句与because of短语的转换Because引导的原因状语从句有时可与because of短语转换，because of后加的原因可以为好或坏但最正规的还是becauseHe can' t come because he is ill. / He can ' t come because of his illness. 他因病不能来。

I said nothing about it because his wife was there. / I said nothing about it because of his wife ' s being there.因为他妻子在那儿，我对此事只字未提。

［考题1］ ___ y ou ' ve got a chanee, you might as well make full use of it.A. Now thatB. AfterC. AlthoughD. As soo n as［答案］A［解析］主句与从句之间存在因果关系，且“ you've got a cha nee”表示一个显而易见的原因，因此应选用表原因的now that。

［考题2］ He found it increasingly difficult to read, ___ his eyesight was beginning to fail.A. andB. forC. butD. or［答案］B［解析］“his eyesight was beginning to fail ” 是“he found it increasingly difficult to read ” 的原因，因此本题应选用可以表示原因的连词for引导原因状语从句。

［考题3］ A man cannot smile like a child, _____ a child smiles with his eyes, while a man smiles withhis lips alone.A. soB. butC. andD. for［答案］D［解析］下划线处之后的句子补充说明“ a man cannot smile like a child ”的原因，应选用for表原因。

原因状语从句练习题I.在下列句子的空格中填入适当的连词（每空一词）：1.________ Jane was the eldest, she looked after the others.2. __________ you know it, I won't repeat it.3.He did n't hear the knock at the door ____________ he was liste ning to the radio.4.—Why did n't you come?—___________ my father would n't let me.5._____________________ everybody is here, let's beg in the discussi on.II.句型转换（把下列复合句转换为简单句）:I）把从句简化为because of结构：1.He lay in bed because he had caught a bad cold.2.He could n't walk because his leg was broke n.3.I came back because it was raining.4.They stayed in because the weather was bad.5.We did n't get home till after midni ght because we had missed the bus.II）把从句简化为分词短语：6.As he is a warmhearted man, he is always ready to help others.7.As he saw n obody in, he decided to leave a no te.8.Because he did n't un dersta nd its meaning, he asked the teacher to expla in the word.9.As he had lived in Beijing for many years, he knew the city very well.10.As I have not see n the film, I can't tell you what I think of it.11.As they were in flue need by Lei Fen g's example, they did a lot of good deeds.12.As he was brought up in the coun tryside, he was not used to the city life.III）把从句简化为形容短语：13.Because he was afraid of being late for class, Bob ran to school as fast as he could.14.As he was full of ear, Crusoe left the cave in a hurry.15.As he was anxious for a quick decision, the chairman called for a vote.Key:1. 1. As2. Since3. because4. Because5. Now that/See ing thatII. 1. He lay in bed because of a bad cold.2.He could n't walk because of a/his his broke n leg.3.I came back because of the rain.4.They stayed in because of the bad weather.5.We did n't get home till after midni ght because of miss ing the bus.6.Being a warm-hearted man, he is always ready to help others.7.Seeing no body in, he decided to leave a no te.8.Not un dersta nding its meaning, he asked the teacher to expla in the word.9.Having lived in Beijing for many years, he knew the city very well.10.Not havi ng see n the film, I can't tell you what I thi nk of it.11.In flue need by Lei Fen g's example, they did a lot of good deeds.12.Brought up in the coun tryside, he was not used to the city life.13.Afraid of being late for class, Bob ran to school as fast as he could.14.Full of ear, Crusoe left the cave in a hurry.15.Anxious for a quick decision, the chairman called for a vote.。