一、作为原因状语,because引导的原因状语从句位置灵活,而for引导的原因状语从句只可在主句之后,如:
1、The doctor looks tired because he sat up all night.=Because he sat up all night,the doctor looks tired 医生看上去很疲劳,因为他整晚都站着。
2、The doctor looks tired , for he sat up all night with the patient.医生看上去很疲劳,因为他整晚都站着。如:
二、由because引导的原因状语分句可以单独用来回答why引导的问句,而for引导的分句不行。
——Why does the doctor look so tired?为什么医生看上去那么累?
——Because he sat up all night.因为他整晚都站着。
三、作为原因状语,because前可带否定词或其他修饰语,还可带某些并列连词,而for分句不可。如:
The doctor looks tired, not because he isn’t feeling well, but because he sat up all night with the patient.医生看上去很疲劳,不是因为他不舒服,是因为他整晚都站着。