for ,because,as,since這四個詞作為連詞,都有"因為"的意思,但它們在用法上有區(qū)別：
because 是從屬連詞,接表示直接原因的從句,一般放在主句的后面,也可放在主句前面,它表示的語氣最強,在回答why的問句時,必須用because.
例如：The swimming pool won't be open today because they're making repairs.
游泳池今天不開放,因為他們在修理.
Why did you move to France?
你們?yōu)槭裁窗岬椒▏?
Because my father found work in Paris.
因為我父親在巴黎找到了工作.
注意：在英語中用了because后,不可再用so.
as 是從屬連詞,說明一般的因果關系,語氣比because弱,說明比較明顯的原因,它引導的從句通常放在句首,有時也可放在句末.
例如：As it is raining,you\'d better take a taxi.
天下雨了,你最好乘出租車.
since 意為"既然",表示對方已知的無需加以說明的原因或事實,語氣比because弱,但是比as 強.
例如：Since we have no money,we can't buy that vase.
既然我們沒錢,我們就不能買那花瓶.
Since everybody is here,let's begin our party.
既然大家都到了,那就開始我們的聚會吧!
for 是并列連詞,用來附帶解釋說明前一分句的原因或理由,for引導的并列句,一般放在所要說明的句子的后面.
例如：I went to see him,for I had something to tell him.
我去見他,因為我有事要告訴他.