英语语法详解：原因状语从句(四大点)
一、引导原因状语从句的从属连词
主要的有because, as, since, seeing (that), now (that), considering (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 can’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。