because as since的区别

because as since都可以用作连词，表原因、理由；

as “因为、既然”表示的原因或理由是明显的。语意不如because强。当理由是明显的，或者被认为是已知的时，则以用as 为好。

because “因为”表直接而明确的原因或理由。即必然的困果关系。

在这几个词中，它的语意最强。回答以why 引导的特殊疑问句时，只能用because。

since“既然”比as 较为正式，说明为人所知的原因。语气比because 稍弱。

As he was not well, I decided to go without him.

因为他身体不好，我决定独自去了

He had to stay at home yesterday because he was ill.

昨天他只得呆在家里，因为他病了

Since he can’t answer the question, you’d better ask someone.

既然他回答不了这个问题，你最好问别人吧。

Since you are busy, I’ll do it for you.

既然你忙，我替你做吧。