1.because表示直接原因,它所指的原因通常是聽話人所不知道的,其語氣最強(qiáng).常用來回答why的提問,一般放于主句之后,也可以單獨(dú)存在.例如：
(1)I stayed at home because it rained.因?yàn)橄掠晡掖粼诩依?
(2)Because Lingling was ill,she didn”t come to school.玲玲因病,沒有上學(xué).
(3)A:Why is she absent?她為什么缺席?
B:Because she is sick.因?yàn)樗×?
此外,在強(qiáng)調(diào)句型中,只能用because.例如：
(4)It was because I missed the early bus that I was late for school.我上學(xué)遲到是因?yàn)槲覜]有趕上早班汽車.
2.since側(cè)重主句,從句表示顯然的或已為人所知的理由,常譯為“因?yàn)椤薄ⅰ凹热弧?語氣比because稍弱,通常置于句首,表示一種含有勉強(qiáng)語氣的原因.例如：
(1)Since he asks you,you”ll tell him why.他既然問你,那就告訴他為什么吧.
(2)Since everyone is here,let”s start.既然大家都到齊了,我們就出發(fā)吧!
(3)Since I understood very little Japanese,I couldn”t follow the conversation.我日語懂得不多,因而聽不懂對話
3.for后可接短語或名詞
(1)We have studied English for years.
我們學(xué)英語已有好幾年了.
(2)They jumped for joy.
他們高興地跳了起來.
(3)Jim is going to get material for a new book.
吉姆正打算為一部新書準(zhǔn)備材料.