原因状语从句

一 because, since,as和for引导的原因状语从句

1 because(因为）：表示直接的原因或理由，着重点在从句，用于回答why，语气最强。

He didn't go to school because he was ill.

Why didn't he go to school? Because he was ill.

2 since(既然）：一般表示对方已知的，无须加以说明的即成事实的理由，全句中心在主句，语气比

because弱。

Since you are ill, I'll go alone.

3 as(由于）：表示十分明显的原因，一般说明因果关系，着重点在主句，语气较弱。

As it is snowing, we shall not go to the park.

4 for(因为，其理由是）：是个并列连词，只能放在另一个并列句后面，表示推理或解释，或用作附加说明，表示新的情况，而不是指理由或原因，语气最弱，一般不放在句首。

The day breaks, for the birds are singing.

* for表示因果关系时，可以同because交替使用，但for前须用逗号，而because则不必。

You couldn't have seen him because he wasn't there.

= You couldn't have seen him, for he wasn't there.

*当原因是显而易见的或已为人们所知，就用as或since，且多放在句首。

Since/ As the weather is so bad, we have to delay our journey.

二 now (that) (既然，现已...所以，当...才）；

Now (that) you've grown up, you should not behave like a child.

Now (that) I am older I see things differently.

Now (that) I have heard the music I understand why you like it.