定语从句中as和which
只用as而不用which：
一、当定语从句置于主句前面时：
例：As you see, the Chinese people are hard-working. (定语从句在句首)
你知道，中国人民是勤劳的。
注意下面句子的多种表达方法：
众所周知，月球每月绕地球转一圈。
1.As is known to everybody, the moon travels round the earth once every month.
2. The moon travels round the earth once every month, as/which is known to everybody.
3. It is known to everybody that the moon travels round the earth once every month.
4.What is known to everybody is that the earth travels round the earth once every month.
(后两句属名词性从句范畴)
二、先行词做主语且定语从句为被动语态时：
此时，从句谓语通常为： be known, be said, be reported， be announced, be mentioned等。如果从句是主动语态，一般用which作主语。
例1：She has been absent again, as is expected.
她又缺席了，这在预料之中。
例2：Tom has made rapid progress, which makes me very happy.
汤姆进步很快，这使我很高兴。
另外，as常用在下列习惯用语中：as (it) seems likely, as (it) often happens, as (it) was printed out, as (it) was said earlier, as I remember (it), as I understand (it), as (it) appears, as it often the case, as anybody can see, as we have expected.
例1：Jack has won the first prize, as it often happens.
像往常一样，杰克得了一等奖。
例2：She has read widely in Romantic Literature, as it appears from her essay ·
她广泛涉猎了浪漫主义文学，这从她的文章中可以看出来。
只用which而不用as
一、关系代词代替前面主句中的宾语从句或定语从句的谓语动词后有复合宾语时：
例：I don't think that he will come to see me, which makes me sad.
我认为他不会来看我了，这使我伤心。
二、which一般用作实义动词的主语，这时它所引导的从句与主句之间存在着逻辑上的因果关系时：
例：Tom was late for school again and again, which made his teacher very angry.
汤姆一次又一次上学迟到，这使得他的老师很生气。
三、当非限制性定语从句是否定句时：
例：He pretended not to know me, which I didn't understand.
他假装不认识我，我真不明白。
四、非限制性定语从句中的be动词不能省略时，用which反之用as.
例1：Jane told me she won the match, which was a lie.
简告诉我她赢了这场比赛，这是谎话。(was不可省略)
例2：As (was) planned, we met at the airport.
按照计划，我们在机场相见了。(was可省略)
as引导的定语从句
在一些习惯用法上，as能兼作关系代词、关系副词，经常引导定语从句。
惯用型1：
such… as…像……一样的`
the same…as…与……同样的
I seldom meetsucha beggarasI met today.
我很少碰到今天这样的乞丐。
（as是代词，在定语从句中作宾语）
Please choosesuchapplesascan be put in my bracket.
请选择我能放入篮子里这样的苹果。
（as在定语从句中作主语）
I am notthe samekind of personasyou are.
我可不是和你一类的人。
（as在从句中作表语）
You may takethe samebusaswe take.
你可乘坐我们坐的同一辆大巴。
（as在从句中作宾语）
惯用型2：
such as…
在这种场合，such是代词，表示“这种人、这种物”，as是关系代词。
He is notsuchasyou can imagine.
他不是你能想象得到的那种人。
We have got a lot of drinkssuchasyou can find in supermarkets.
我们习了大量在超市能找到的那种饮料。
惯用型3：
as…
…, as…
as引导的定语从句，有时像非限制性定语从句一样修饰整个主句或者主句的一部分，但它的位置比较灵活，可以放在被修饰的主句后面，也可以放在主句前面。
例如：
Asyou can see, we are all students.
你能看得出，我们都是学生。
=We are allstudents,asyou can see.
=We are all students,whichyou can see.
（这是详细的解读，大家请熟悉啊）
Asyou know, we need to hurry up.
大家知道，我们需要加快速度。
He is not very honest,asyou have proved.
她不是很诚实，这一点你已证实了。
定语从句中which
Which引导的定语从句在语法和语用功能有利于区别于that引导的定语从句的鲜明特色.
一、语法要点.
①有宽阔的指代范围.不仅可措代主句中某一先行词___名词（A）,还可以指代主句中某些句子成分,如不定式宾补,不定式宾语,动宾结构等（B）,甚至整个主句
（C）.后两项功能是that所没有的.
（A）The computerwhich(=that) I bought yesterday is home made.
（B）Yesterday I asked him to go to the cinema with me,whichagreed(昨天我要他同我一道去看电影,他同意了).
He wishes to get quick rich without any labour,whichwe think only Wishful thinking (他想不劳而获,迅速致富,我们认为这是想入非非).
（C）The sun heats the earth,Whichis very important to living things(太阳晒热地球,这对于万物是十分重要的).
②非限定性定语从句中,无论主语还是宾语,关系代词用which不用that;即使which作宾语也不省去.
Football,whichis very interesting, is played all over the world.
I never give up learning foreign languages.WhichI fink to de a bridged to the world(我从没有放弃过外语学习,因为我发现外语是通向世界的桥梁).
（比较下一句关系代词作宾语可省去的限定性定语从句.二者在这一点上的区别一目了然：It is the computer (that /which) I bought last week.）
③“介词+关系代词”引导定语从句有一下四点值得注意.
A:当介词前置时,关系代词用which而非that；而且which不省去.
The pencil with he was writing broke.
无The pencil with that he was writing broke;也无The pencil with he was writing broke.
(注：当介词后置于定语从句动词后面,并且从句是定性的,关系代词which, that可互换,能省略.This is the roomwhich/that the great man once worked in.)
B:先行词表示时间,定语从句可用关系副词（when;先行词表示地点,定语从句可用关系副词where:
We’ll never forget the day onwhich(-when )we visited the Great wall.
They went to the village where(-atwhich)the oil well was located定位）.
C：此结构再延伸,出现“名词/代词+of/among+关系代词”的格局,名词又有数量意义,如“许多,一些,大部分,20个等”,则整个短语译作“其中许多；其中一些…”：
On the crowded bus were school children, many of whom were from Beijing.
也可以把名词/代词称到关系代词后面,整个短语的功能不变：
He borrowed from the library novels and magazines, amongwhichsome are in English.
D:此延伸结构若是“名词+介词of+关系代词”的格局,名词无数量意义,则同于whose+名词：
He lives in the house the doors ofwhichface the south,=He lives in the house whose doors face the south.
二、语用功能.
Which定语从句（尤其是非限定性的）主要还是在语用功能上呈现that定语从句所没有的亮点.
①表达主从句因果关系.
A Jew. Albert Einstein had to flee Germany.Whichthen was ruled by Hitler(爱因斯坦只得逃离德国,因为当时的德国是在希特勒的统治之下).
NMET’99：Cory Luxmoore arrived from England to deliver the diary of his ancester to the Library Company,____he and his wife considered to be the best home for the diary (Cory Luxmoore（千里迢迢）从英国赶来把祖先的日记交给（费城）图收馆公司,是因为他和妻子认为该图书馆才是此日记最好的归宿处).
②表达主从句目的关系.
The Southern States set up a separate state of their own, inwhichthey would be free to keep Negroes as slaves(南方各州却反叛建立一个独立王国,以便好继续维持奴隶制度).
③表达主从句让步关系.
Einstein, who could have been very rich, cared for little money(爱因斯坦原本可以是非常富有的,但他却不爱钱).
He gave up his cause inwhichhe had been very successful and joined in our project(他的事业尽管干得很出色,他还是放弃了,加入到我们的课题研究中来).
④表达主句动作产生的结果.
Many trucks and buses are jammed at the crossing,whichmade it impossible for us to go to work on time(许多车辆都堵在十字路口,造成我们不能准时上班).
European football is played in 80 countries,whichmakes it the most Popular sport in the world(欧式足球有30个国家在踢,因之成为全世界最流行的一项体育运动).
⑤表示主从句条件关系.
The past experience,whichis not forgotten, is the guide for the future(前事不忘,可为后事之师).
⑥表示主从句时间关系.
He was born on October 1,1949,whichsaw the foundation of the People’s Republic of China(他出身在一九四九年十月一日,恰好是中华人民共和国成立的那一天).
⑦对主句内容作补充说明.
Inspite of his glorious past, he has fallen into the people’s enemy at last,whichis a good lesson for all of us (尽管有着辉煌的过去,他最终还是堕落为人民的敌人,这对我们大家是个很好的教训).
The sentence was announced on Nov. 8 following trials,whichstarted in Sept.(审判于九月开始.多次审判后,判刑才于十一月八日宣布).
⑧用于主从句对比关系.
He idled away his youthwhichhe should have spent in leaning(他的青春年华本应用于增长才干,而他却虚度过去了).
⑨用于表示世界上独一无二的人或事物；或当事人认为是独一无二的事物.
China,whichhas a 5000_year_old civilization, is now taking a new
Look(已有5千年文明的中国现在正呈现新面貌).
All the books here,whichhave beautiful pictures in them, were written by him(这里所有的书都是他写的,里面都有精美的插画).
（比较：All the books here that have beautiful pictures in them were written by him (这里所有有着漂亮插画书是他写的__这里不仅关系词要换成that,而且还暗示着有虽的书)）.
⑩表示与主句或先行词的同位关系.
The speed of sound in air at ordinary temperature is about 1,100 feet per second,whichis about 700 miles per hour(常温下声在空气中的速度是大约每秒1,100英尺,即大约是小时传播700英里远.)
可以看出,which定语从句不仅涵盖that定语从句的功能__即纯定语功能,而且还有that定语从句所不能表达语用领域___状语用法.因此,只注意which定语从句的语法搭配而忽略其语用意义,就意味着对英语定语从句的认识还没有到位.
