【编者按】除了下面A2，A3中所示各种类型外，这两种从句均可由as或because来引导。但是用as引导原因从句较为稳妥(参见A);用because引导结果/原因从句较为稳妥(参见B)。
A 原因从句
1 由as/because/since 引导的原因从句：
We camped there as/because/since it was too dark to go on.
我们在那里露宿是因为天太黑，不能再继续往前走了。
As/Because/Since it was too dark to go on，we camped there.
因为天太黑不能再继续往前走，我们就在那儿露宿了。
2 in view of the fact that可用as/since/seeing that来表示，但不能用because：
As/Since/Seeing that you are here，you may as well give me a hand.
既然你在这儿，你就帮我个忙吧。
As/Since/Seeing that Tom knows French，he’d better do the talking.
既然汤姆懂法语，最好让他来谈。
3 在as/since/seeing that意指以前共知的或共知的陈述时，可用if来代替：
As/Since/Seeing that/If you don’t like Bill，why did you invite him?
既然/如果你不喜欢比尔，你为什么邀请了他?
注意：if so的用法：
—I hope Bill won’t come.
—If so(=If you hope he won’t come)，why did you invite him?
—我希望比尔别来。
—如果这样(=如果你希望他不来)，你为什么邀请了他?
关于if+so/not，参见第347节。
B 结果从句(参见第339节)由because或as引导：
The fuse blew because we had overloaded the circuit.
保险丝烧断了，因为我们使线路超载了。
He was angry because we were late.
他生气是因为我们来晚了。
As it froze hard that night there was ice everywhere next day.
因为那天晚上冷得厉害，所以第二天到处都是冰。
As the soup was very salty we were thirsty afterwards.
因为这汤很咸，后来我们渴得厉害。
C 这种组合也可用so连接两个主句的形式来表示：
It was too dark to go on，so we camped there.
天太黑了，不能继续往前走了，所以我们就在那儿露宿了。
You are here，so you may as well give me a hand.
你们既然在这儿，不如就帮我一下。
It froze hard that night，so there was ice everywhere next day.
那天夜里冷得厉害，所以第二天到处都是冰。
也可以使用therefore，但只限用于非常正式的句子中：
The Finnish delegate has not yet arrived.We are therefore postponing/ We have therefore decided to postpone/Therefore we are postponing the meeting.
芬兰代表还没有到达。我们因此要把会议推迟/因此我们已决定把会议推迟/因此我们要把会议推迟。(注意therefore可以放在几个不同的位置。)
such/so…that引导的结果从句
A such是形容词，用于形容词 名词结构之前：
They had such a fierce dog that no one dared to go near their house.
他们有一条如此凶猛的狗，以致没人敢靠近他们家。
He spoke for such a long time that people began to fall asleep.
他说了这么长时间，以致在座的人都犯困了。
B so是副词，用于副词和不带名词的形容词之前：
The snow fell so fast that our footsteps were soon covered up.
雪下得这么快，以致我们的脚印很快就被雪盖住了。
His speech went on for so long that people began to fall asleep.
他的讲话这么长，以致在座的人都开始犯困了。
Their dog was so fierce that no one dared come near it.
他们的狗太凶猛了，所以没人敢靠近它。
但such不能用于much和many之前，所以so可用于后跟名词的much和many之前：
There was so much dust that we couldn’t see what was happening.
灰尘太大了，使得我们看不清发生了什么事。
So many people complained that they took the programme off.
抱怨的人太多，所以他们取消了那个节目。
C 注意：such+a+形容词+名词可由so+形容词+a+名词来代替，所以such a good man可由so good a man来代替。这只能在名词前面有a/an的情况下使用。这种形式不常见，但有时出现在文学作品中。
有时为了表示强调，so位于句首。这时后面跟动词的倒装形式(参见第45节)：
So terrible was the storm that whole roofs were ripped off.
暴风真可怕，把整个的屋顶全都刮飞了。
让步从句
它们由下列词来引导：although，though(参见第327节与第329节)，even though，even if，no matter，however(参见第85节)。有时也可以使用whatever。as也可以，但是只限于形容词+as+be结构。
Although/Though/Even though/Even if you don’t like him you can still be polite.
尽管/即使/纵然/即使你不喜欢他，你仍可有礼貌一些。
No matter what you do，don’t touch this switch.
无论怎样，都别碰这个按钮。
However rich people are，they always seem anxious to make more mon- ey.
无论人们多么富有，他们似乎总还渴望赚到更多的钱。
However carefully you drive，you will probably have an accident eventual- ly.
无论你开车多小心，最后你大概还会出车祸。
Whatever you do，don’t tell him that I told you this.
无论如何，别跟他说这件事是我告诉你的。
Patient as he was，he had no intention of waiting for three hours.
哪怕他再有耐心，也不打算等上三个小时。
may+动词原形可用于假设情况：
However frightened you may be yourself，you must remain outwardly calm.
无论你有多害怕，外表上你仍要保持冷静。
may含有I accept the fact that(我接受这一事实)的意思：
—But he’s your brother!
—He may be my brother but I don’t trust him!
—可他是你的兄弟!
—尽管他是我的兄弟，可我不信任他!
但may这样用时，是另一主句的一部分，并不属于让步从句之列。should+动词原形结构可用于even if之后，正如用于条件句的if之后一样，用来表示should后面的动词原形所指的动作不太可能发生：
Even if he should find out he won’t do anything about it.
即便他发现了，他也不会采取什么行动的。
比较从句
A 形容词和限定动词连用时的比较(另参见第20节至第22节)：
It’s darker today than it was yesterday.
今天比昨天天色昏暗。
He doesn’t pay as much tax as we do/as us.
他没我们交的税款多。
He spends more than he earns.
他花的比挣的多。
注意：that+形容词是一种口语形式，表示“那么……”：
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