原因狀語從句

比較：because, since, as和for

1）because語勢最強，用來說明人所不知的原因，回答why提出的問題。當原因是顯而易見的或已為人們所知，就用as或 since。 I didn't go, because I was afraid. Since /As the weather is so bad, we have to delay our journey.

2）由because引導的從句如果放在句末，且前面有逗 號，則可以用for來代替。但如果不是說明直接原因，而是多種情況加以推斷，就只能用for。 He is absent today, because / for he is ill. He must be ill, for he is absent today.