1.because引导的原因状语从句

(1)由because引导的原因状语从句通常表示说话人或作者认为这种原因是听者或读者所不知道的，因此在回答以疑问词why开首的问句时，只能用because，而不能用since或as。此外，在强调句中只能用because，而不能用since或as。

—Why didn't you come?

——你为什么没有来?

—Because I was ill．

——因为我病了。

It was because he was ill that he didn't go with us．

是因为他病了才没有跟我们一块儿去。

提示：

用了because就不要用so了，英语书面语有一个基本原则，就是两个句子(或者称为分句)由且仅由一个连词引导，下面的句子就是错误的:

Because he was ill，so he missed the class．

(2)由because引导的原因状语从句既可置于主句之前，也可置于主句之后，主从句之间既可用逗号隔开，也可不用逗号。

Some people can never go above 4，000 metres because their body is unable to adjust to these extreme conditions．(人教大纲版高三第16页)

有些人从来不能登上4 000米的高度，因为他们的身体不能适应这些极端的条件。

He distrusted me because I was new．

他不信任我，因为我是新来的。

He didn't buy it，because it was expensive．

他没有买是因为它太贵了。

Because it was wet，I didn't go out for a walk．

因为外面是湿的，我没有出去散步。

提示：

because引导的从句有时不是修饰主句的整个谓语(或整个主句部分)，而是修饰谓语的一部分，表现在主句是否定句时，用在主句之后的because须用逗号隔开才能明确表示该从句修饰主句的整个谓语，若不用逗号隔开，在书面语中有的时候容易引起歧义。

He is only sick in mind because he is sick in body．

=He is sick in mind only because he is sick in body．

他精神失常，只不过是因为他身体有病。

I didn't leave home because I was afraid of my father．

该句可能有两种解释:①我并不是因为怕父亲才离开家的。(not否定because从句)②因为我怕父亲，所以没有离开家。(not否定主句的整个谓语)

当然，在上下文清楚的情况下，就不存在歧义了。

The studio didn't really like the script of Nosebleed because it was not perfect yet．(人教大纲版高一上第112页)

制片厂不怎么喜欢《流鼻血》这个剧本，是因为它还不是很完美。

另外，在because之前可以加上only，simply，just，partly等强调语。

People read advertisements partly for information and partly because they are interesting．(人教大纲版高三第44页)

人们看广告的部分原因是想从中获取信息，还有一部分原因是广告很有意思。

Fish can live in these temperatures only because their blood contains a particular chemical．(95人教版高二下第22页)

鱼能生活在这样的温度环境中仅仅是因为它们的血液中有一种特别的化学物质。

(3)because与for用法比较。

表示因果关系的并列连词for，从用法上看，兼有并列连词和从属连词的某些特征。但是for引导的句子(可以理解为从属连词，也可以理解为并列连词)的位置是固定的，通常位于主句之后，而且要用逗号隔开，与并列句很相似。

The old lady doesn't go out in the winter，for she feels the cold a great deal．

这个老太太冬天不出门，因为她觉得太冷了。

The morning had been fine，for there was no wind．(人教大纲版第79页)

早晨天气很好，没有刮风。

because和for都可以表示原因，但多数场合because和for不宜互换，它们的区别可以从三方面来说明:

①从性质上说，because是从属连词，连接原因状语从句;而for是并列连词，连接两个并列句。

②从意义上说，because从句表示的是客观的、直接的原因;而for从句表示的只是主观推断的依据。

It's going to rain，because the dark clouds are gathering and hanging lower and lower．

就要下雨了，因为乌云密布，而且越压越低了。

It's going to rain，for my knee joints are aching．

就要下雨了，因为我的膝关节酸痛。

The day breaks，for the birds are singing．

天亮了，你听，鸟儿在唱歌。

He must be in the room，for the light is on．

他准在房间，你瞧，灯亮着。

The days were short，for it was December．

白天的时间很短，你想啊，是十二月了。

③从句法上说，第一，because引导的从句可以放在主句之前，也可以放在主句之后;但是for引导的从句只可放在主句之后。

She was so depressed because she failed the exam．

=Because she failed the exam，she was so depressed．

她很沮丧，因为考试没及格。

She must be depressed，for she failed the exam．

她一定很沮丧，因为考试没及格。

×For she failed the exam，she must be depressed．

第二，because状语从句可以用于“It is(was)．．that．．”强调句型中，而for从句则不能。

It was because I worked so hard that I was promoted last month．

我上个月得到提升是因为我工作努力。

×It was for I worked so hard that I was promoted last month．

第三，because可以引导表语从句，还可用副词来修饰，如merely because，only because，simply because等;而for从句不可作表语，也不能用副词来修饰。

It is chiefly because he is too impatient．

这主要是因为他太没耐心的缘故。

×It is chiefly for he is too impatient．

He was fired simply because he was too careless．

他被解雇就是因为太粗心。

×He was fired simply for he was too careless．

第四，because状语从句可以置于not之后，还可以用一定的并列连词形成并列的because从句。

I gave him the permission，because I had to，not because I wished to．

我给了他许可，因为我必须这样做，而不是我想这样做。

He was late with his homework，not because he couldn't do it，but because he was ill．

他迟交了作业，不是因为他不会做，而是因为他病了。

I like the story because it was the first time that I had written with real passion and because it made me realize that everyone's life is different．(人教大纲版高二上第12页)

我之所以喜欢这篇报道，是因为这是我第一次满怀热情去写的，这使我认识到每个人的生活都各具特色。

第五，连词for可以引导一个独立的句子，为前一句话或上一段所陈述的情况说明原因或提供理由，而because引导的状语从句，除了用以回答why开头的问句外，较少单独存在。

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

当我看见她在河水中的时候，我很替她害怕。在那个地方，水流很危险。