原因狀語從句雖然沒有其他狀語那么復(fù)雜，連詞總類也比不上其他狀語從語那么多，但是也是有一些容易混淆的連詞，because，for，since，as在原因狀語從句中意思幾乎一樣，翻譯成中文也往往都翻譯成”因?yàn)椤埃欢@四個(gè)詞在使用上其實(shí)也是有著一些微妙的差別的。

一. because引導(dǎo)的原因狀語從句一般放于主句的后面，because從句位于句首時(shí)要用逗號(hào)分開，放在句末時(shí)，可不用逗號(hào)分開。because表示直接原因， 語氣最強(qiáng)， 最適合回答why引導(dǎo)的疑問句。because of 也表示原因，但它后面不接從句, 只能接名詞, 代詞或動(dòng)名詞。注意：because 和so 不可同時(shí)出現(xiàn)在一個(gè)句子里。
I do it because I like it. = I like it so I do it.
We went by bus because it was cheaper. = It was cheaper so we went by bus.
He can’t go to school because of his illness.

二. since引導(dǎo)的原因狀語從句一般放于主句之前表示已知的、 顯然的理由(通常被翻譯成“既然”= now that )， 較為正式， 語氣比because弱。
Since you are free today, you had better help me with my mathematics.
Since you don't trust him, you should not employ him.
Now (that) you are grown up, you should not rely on your parents.

三. as 引導(dǎo)原因狀語從句時(shí)表示附帶說明的“雙方已知的原因”，含有對(duì)比說明的意味，語氣比since弱， 較為正式， 位置較為靈活(常放于主句之前)。
As it is raining, you’d better take a taxi.
As you are tired, you had better rest.
I went to bed early, as I was exhausted.

四. for引導(dǎo)的是并列句表示原因但并不說明主句行為發(fā)生的直接原因， 只提供一些輔助性的補(bǔ)充說明， for引導(dǎo)的并列句只能放于主句之后并且必須用逗號(hào)將其與主句隔開。
He could not have seen me, for I was not there.
He seldom goes out now, for he is very old.

怎么樣，大家都get到了這四個(gè)詞之間的細(xì)微差別嗎？文字說明看起來可能有些復(fù)雜，但多讀幾遍例句就能很快的理解了！大家在學(xué)習(xí)的過程中要多加注意哦，千萬不能放過一絲一毫的小細(xì)節(jié)！