有时为了使语言的精炼，达到言简意赅的效果, 我们常将状语从句进行"简化"。状语从句的"简化"现象在口语中很普遍, 因此,有必要对其进行全面、透彻的了解。
状语从句同时具备下列两个条件:
① 句和从句的主语一致，或从句主语为it；
② 从句主要动词是be的某种形式。从句中的主语和be动词常可省略。
例如：
When ( the museum is ) completed , the museum will be open to the public next year .
博物馆建成后，明年将向公众开放。
He’ll go to the seaside for his holiday if (it is ) possible.
如果可能的话，他将去海边度假。
另外，比较状语从句经常省略。例如：
I’m taller than he (is tall ).
The higher the temperature (is), the greater the pressure (is ).
状语从句的"简化"现象常存在于以下五种状语从句中:
①由if, unless等引导的条件状语从句;
②由although, though, even if / though等引导的让步状语从句;
③由when, while, as, before, after, until / till等引导的时间状语从句;
④由as, as if等引导的方式状语从句;
⑤由as, than等引导的比较状语从句。下面给予归纳：
(1)当状语从句的主语是it,且谓语动词是be时,it和be要完全简化掉。
例如:
If (it is) possible, he will help you out of the difficulty.如果可能的话,他会帮你摆脱困境。
You must attend the meeting unless (it is) inconvenient to you.除非情况对你来说不方便,否则你必须出席这次会议。
(2)当状语从句的主语和主句的主语一致时,从句可以将主语和be动词简化掉。常用于以下几种情形:
a.连词+形容词
As (he was) young, he learned how to ride a bike.他小时候就学会了骑自行车。
Work hard when (you are) young, or you'll regret.少壮不努力,老大徒伤悲。
Whenever (she is) free, she often goes shopping.
她有空就去逛商店。
b.连词+名词
Although (he was) a farmer, now he is a famous director.尽管他曾是个农民,而现在是位著名的导演了。
While (he was) a young boy, he was always ready to help others.
他在孩子时代就乐于助人。
c.连词+现在分词
Although (he is) doing his best in maths these days, he has still got no good marks.尽管近来他一直在学数学,但他仍然没有取得好成绩。
As (she was) walking along the river bank, she was singing a pop song.
她沿着河堤边走边唱着流行歌曲。
Sam lost his wallet while he was taking his savings to the post office.
Sam lost his wallet while taking his savings to the post office.或：
While taking his savings to the post office, Sam had lost his wallet.
萨姆在把存款带到邮局时丢了钱包。
Since I came to Beijing, I have made many new friends.
=Since coming to Beijing, I have made many new friends.
自从我来到北京以来，我交了很多新朋友。
After I finished my homework, I fed the dog.
=After finishing my homework, I fed the dog.
我做完作业后，给狗喂食。
d.连词+过去分词
He won't go there with us unless (he is) invited.除非受到邀请,否则他不会和我们一道去那里。
The concert was a great success than (it was) expected.这场音乐会出乎意料地取得了巨大成功。
A zero can have its meaning only when (it is) used with real numbers
零只有在与实数一起使用时才有意义。
e.连词+不定式
He stood up as if (he were) to say something.当时他站起来好像要说什么。
He wouldn't solve the problem even if (he were) to take charge.即使他来负责,他也解决不了这个问题。
f. 连词+介词短语
She looked anxious as though (she was) in trouble.她看上去很焦急,好像遇到了麻烦。
He had mastered the English language before (he was) in the USA.他到美国之前就懂英语了。
注意:当从句主语和主句主语不一致时,从句部分要么用完全形式,要么用独立主格结构来表达。独立主格结构主要表示谓语动词发生的时间、原因、条件或伴随情况等，相当于一个状语从句或并列句。
用作时间状语
After the work had been done, we went home.
The work done, we went home.
工作完成后，我们就回家了。
After the meeting was over, all of us went home.
The meeting being over, all of us went home. 开完会后我们都回家了。
用作条件状语
If weather permits, they will go on an outing to the beach tomorrow.
Weather permitting, they will go on an outing to the beach tomorrow.
如果天气允许的话，他们将在明天组织一次海滨小游。
If the condition is favourable, he may succeed.
The condition being favourable, he may succeed.
若条件有利,他或许能成功。
用作原因状语
As an important lecture will be given tomorrow, the professor has to stay up late into the night.
An important lecture to be given tomorrow, the professor has to stay up late into the night.
因为明天要发表一个重要的演讲，教授不得不熬夜到很晚。
He wrapped her up with great care because the night was dark and frosty.
He wrapped her up with great care, the night being dark and frosty. 夜又黑又冷,所以他把她裹得严严实实的。
用作伴随状语
He was lying on the grass, and his hands were crossed under his head.
He was lying on the grass, his hands crossed under his head.
他躺在草地上，将两手交叉枕在脑后。
用作让步状语
Though she worked so hard, she failed again.
Working so hard, he failed again.
尽管努力，他还是失败了。
让步状语从句简化后也有其他形式，比如不定式或独立主格或介词短语！
许多时候的简化，就是把状语从句的动词根据主动与被动需要处理成从属性的ing形式或过去分词或不定式形式即可。且连词往往可以省略。
When the city is seen from the top of the hill, it looks very small.
Seen from the top of the hill, the city looks very small.
当从山顶看到这座城市时，它看起来很小。
Since I have finished my work for today, I will go out for a long walk.
Having finished my work for today, I will go out for a long walk.
既然我完成了今天的工作，我就出去散散步。