原因状语从句一、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：
The woolly shrank because it was washed badly. 毛衣因洗得不得法而缩水。
I can’t get to sleep because of the noise outside. 由于外面声音嘈杂我睡不着。
Since [As] we’ve no money, we can’t buy it. 由于我们没钱，我们无法购买它。
Seeing that it’s raining, we’d better stay indoors. 既然外边在下雨，我们最好待在室内。
Now that you are here, you’d better stay. 你既然来了，最好还是留下吧(既来之，则安之)。
【注】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。
二、关于not…because结构
该结构中的否定词有时否定主句，有时否定从句，一般要根据句子的意思作出正确或合乎逻辑的理解。若not否定主句，最好在because之前用逗号，否则会引起歧义，如下句在没有特定上下文时就有两种解释：
I didn’t go because I was afraid. 我没有去是因为怕。/ 我不是因为怕才去。
不过若because之前有just修饰，一般认为not 是否定从句的：
You shouldn’t get angry just because some people speak ill of you. 你不要因为有人说你坏话而生气。
三、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.
四、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：
He 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。
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.
用法原因状语从句表原因， 以下逐一介绍高考中常见的原因状语从句的引导词：
1. 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 country is not strong because it is large. 国强不在大。
2. 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： seeing (that)， now (that)， considering (that)， in that这几个词汇与since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。
3. 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。
4. 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。
考题解析［考题1］ ____ you’ve got a chance, you might as well make full use of it. (1999)
A. Now that B. After C. Although D. As soon as
［答案］ A
［解析］ 主句与从句之间存在因果关系， 且“you’ve got a chance”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. (2006北京)
A. and B. for C. but D. 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 with his lips alone. (2006湖南)
A. so B. but C. and D. 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。
