第1个回答 2015-12-09
because／since／as／for这四个词都是表示原因或理由的连接词,但是as,because,since是从属连词,引导原因状语从句,for是并列连词,所引导的不是原因状语从句,而是表示理由的对等句子,是对前面所讲内容补充和说明.在语气上由强至弱依次为because→since→as→for.because引导的从句多置于句末,表示直接的原因或理由,表示产生那种结果的必然的因果关系,在回答why的提问时,必须用because作答.
如：We stayed at home because it rained．因为下雨我们呆在家里.
as与since引导的从句多置于句首,不过as表示十分明显的原因,只说明一般的因果关系,可译为“因为、由于”；而since则表示稍加分析、对方已知的原因,一般可译为“既然”.如：
As he was not feeling well,I decided to go there alone．由于他身体欠佳,我决定独自去那里.
Since everyone is here,let';s start．既然大家都到了,咱们就开始吧.
for引导的分句一般放在句末,其前用逗号,它所叙述的理由是间接的,即推测性理由,或是对前面叙述的事实或看法的补充说明.如：
There must be nobody in the classroom,for the light is off．教室里一定没有人,因为灯灭了.（推测性理由）转自网上,供参考：
because,since,as,for
because／since／as／for这四个词都是表示原因或理由的连接词,但是as,because,since是从属连词,引导原因状语从句,for是并列连词,所引导的不是原因状语从句,而是表示理由的对等句子,是对前面所讲内容补充和说明.在语气上由强至弱依次为because→since→as→for.because引导的从句多置于句末,表示直接的原因或理由,表示产生那种结果的必然的因果关系,在回答why的提问时,必须用because作答.
如：We stayed at home because it rained．因为下雨我们呆在家里.
as与since引导的从句多置于句首,不过as表示十分明显的原因,只说明一般的因果关系,可译为“因为、由于”；而since则表示稍加分析、对方已知的原因,一般可译为“既然”.如：
As he was not feeling well,I decided to go there alone．由于他身体欠佳,我决定独自去那里.
Since everyone is here,let';s start．既然大家都到了,咱们就开始吧.
for引导的分句一般放在句末,其前用逗号,它所叙述的理由是间接的,即推测性理由,或是对前面叙述的事实或看法的补充说明.如：
There must be nobody in the classroom,for the light is off．教室里一定没有人,因为灯灭了.（推测性理由）本回答被提问者采纳
第2个回答 2015-12-09
since, as because,for都可表示原因，它们的区别是：
1. Becasue：当原因作为句子或陈述最重要的一部分时，我们使用because.
Because通常出现在句首部分。
Because is used when the reason is the most important part of the sentence or utterance. The because clause usually comes at the end:
e.g. I went to Spain last summer because I wanted the guarantee of sunshine on every day of my holiday.
2. As和since：当原因是众所周知时，我们使用as和since，因此，这样的原因一般不那么重要。
as或since从句一般置于句首。
As and since are used when the reason is already well known and is therefore usually less important. The as or since clause is usually placed at the beginning of the sentence:
e.g. As the performance had already started, we went up to the balcony and occupied some empty seats there.
e.g. Since John had already eaten, I made do with a sandwich.
3. For：For意味着原因是事后给出的。
For从来都不会置于句首，带有书面英语而非口语的色彩。
For suggests that the reason is given as an afterthought. It is never placed at the beginning of the sentence and is more characteristic of written, rather than spoken English:
e.g. I decided to stop the work I was doing - for it was very late and I wanted to go to bed.
来源：
http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv27.shtml
第3个回答 2015-12-09
since, as because,for都可表示原因，它们的区别是：
1. Becasue：当原因作为句子或陈述最重要的一部分时，我们使用because.
Because通常出现在句首部分。
Because is used when the reason is the most important part of the sentence or utterance. The because clause usually comes at the end:e.g. I went to Spain last summer because I wanted the guarantee of sunshine on every day of my holiday.
2. As和since：当原因是众所周知时，我们使用as和since，因此，这样的原因一般不那么重要。
as或since从句一般置于句首。
As and since are used when the reason is already well known and is therefore usually less important. The as or since clause is usually placed at the beginning of the sentence: e.g. As the performance had already started, we went up to the balcony and occupied some empty seats there.e.g. Since John had already eaten, I made do with a sandwich.
3. For：For意味着原因是事后给出的。
For从来都不会置于句首，带有书面英语而非口语的色彩。
For suggests that the reason is given as an afterthought. It is never placed at the beginning of the sentence and is more characteristic of written, rather than spoken English:e.g. I decided to stop the work I was doing - for it was very late and I wanted to go to bed.