想要掌握原因状语从句，就要准确理解它的从属连词的意义和用法，以及不同从属连词之间的用法区别，小编为大家准备了一系列的解析，一起来看看吧！

由because引导的原因状语从句可单独用来回答why-问句，而for-分句不可以。

例如：

—Why does the doctor look so tried and sleepy?

—Because he sat up all night with patient.

作为原因状语，because-分句可在because之前带否定词或其他修饰语，还可以带某些并列连词，而for-分句不可以。

例如：

The doctor looks tried and sleepy simply because he sat up all night with the patient.

The doctor looks tried and sleepy not because he isn’t feeling well, but because he sat up all night with the patient.

第四，作为原因状语，because-分句可作为分裂句中心成分，而for-分句不可以。

例如：

It is because he sat up all night with the patient that the doctor looks tried and sleepy.

以上所言because-分句与for-分句用法上的区别仅就代表“直接理由”即为某一事实说明原因这一用法而言。如果because-分句表示“直接理由”，即对说话人为何说这种话提出理由，那么这种because-分句，和for-分句一样，只能位于主句之后，既不能用以回答why-分句，也不能在because之前用否定词或其他修饰语，当然也不能作分裂句中心成分。

连词for还可以引导一个句子，为上文陈述的情况说明或提供理由，而because-分句通常引导从属分句，除了用于回答why-问句以外，because-分句通常不单独出现。

例如：

When I saw her in the river, I was frightened. For at that point the currents were dangerous.

The men’s and the women’s shops are indistinguishable from each other. For the women’s shop windows dispaly masculine shirts, while the men’s windows are full of scarlet miniunderpants.

连词for的这一用法，和其他一些用法一样，使它近似于并列连词。所以，如前所述，连词for是介乎从属连词与并列连词之间的。正因为连词for具有并列连词的某些连词的某些特征，所以当它连接两个分句时，按照正式书写规则通常要在for-分句之前用逗号隔开。

例如：

He was glad to go, for the hostess had been especially good to him.

Something fell in, for I heard a splash.

不过这条规则在当代英语中并不严格遵守，尤其在非正式语体中。

看完了解析，有没有觉得豁然开朗呢？这类小有困难的语法知识需要大家多回顾、多思考，赶快收藏起来多看看吧~