As 的非限制性定语从句引导词用法例
As 的用法例
1. the same… as；such…as 中的as 是一种固定结构, 和……一
样……。
I have got into the same trouble as he (has).
2. as可引导非限制性从句，常带有'正如'。
例1.As we know, smoking is harmful to one's health.
例2.As is known, smoking is harmful to one's health.
As是关系代词。例1中的as作know的宾语；
例2中，它充当从句的主语，谓语动词know要用被动式。
一、“as / which” 特殊定语从句的先行成分
1. 形容词或形容词短语作先行成分, 具有形容词意义的介词短语
也可以充当先行成分，如：
My grandmother’s house was always of great importance to me, as my
own is.
在一定的语言环境里，有些名词可以具有形容词的性质。这些名词
主要是那些表示人的身份、职业、状态的名词。值得一提的是，在这
些具有形容词性质的名词之后，引导定语从句的关系代词不能用who
/ whom.
2. 动词短语先行成分。
这种动词短语既可是限定形式也可是非限定形式。如果是动态动词
短语，它们在从句中就一般有限定或非限定形式的替代动词do和as /
which一起代替。do可以出现，也可以不出现，但不能用其它动词代
替。
3. 句子作先行成分。
这句子可以是整个主句也可以只是主句中的一个从句。有时是连续
几个句子，有时甚至可以是一个完整的故事。
二、“as/which”特殊定语从句在句中的位置
由于先行成分的构成成分不同，“as/which”特殊定语从句在句中的
位置有以下几种情况：
1. 形容词做先行成分时：形容词或形容词短语（含具有形容词性
质的名词）作先行成分，“as / which”特殊定语从句置于先行成分之后。
2. 动词短语作先行成分时：动词短语作先行成分时，“as / which”
特殊定语从句置于先行成分之后。但是，当从句中含有表示主观意志
的插入成分时，“as”特殊定语从句可以移至句子之首。
3. 句子作先行成分时：“as”特殊定语从句的位置较灵活，可以置于
先行成分之前、之中或之后。但如果先行成分是直接引语，“as”特殊
定语从句多在先行成分之前。如果先行成分是否定句，“as”特殊定语
从句与否定词的相对位置不同可以使它产生不同的意义。由于“as”特
殊定语从句具有这一特点，所以有时它的位置不能随便移动。在非正
式的文体里，“which”特殊定语从句可以出现在先行成分之中。
三、“as/which”特殊定语从句的语义功能
一般说来，as与which的语义功能相同，可以相互替换。但先行成
分为句子时，它们的语义功能则有差异。
1. 表示结果
表示结果的特殊定语从句与其先行成分之间存在着一定的因果关
系，从句中往往使用有结果意义的词，如动词result, make, enable,
cause和形容词interesting, surprising, delightful, disgraceful等。
2. 表示评注
表示评注的特殊定语从句对其先行成分所述事实的正确性有肯定
的倾向，它通常与那些表示客观事实，普遍真理或某种习性的先行成
分连用；从句中则常用一些表示“合乎自然规律”、“众所周知”或“经
常发生”等意义的词语，如natural, known to all, usual等。
3. 有无状语意义
“as”特殊定语从句具有状语意义（主要是方式状语意义），而“which”
特殊定语从句则无状语意义。“as”特殊定语从句的状语意义要求它在
语义上与其先行成分的语义保持一致，“which”特殊定语从句则不受
这种限制。
四、关系代词as与which的句法功能
1. as / which 在特殊定语从句中作主语。
as作主语时，谓语动词常为连系动词（主要是be, seem），主语补
语为usual、 a rule、 a matter of fact等时，系动词be习惯经常省略。
行为动词作“as”特殊定语从句的谓语时一般用于被动语态（其中助动
词be常略），不及物的行为动词在“as”特殊定语从句中作谓语的极少，
常见的有happen一词。如：
Freddie, as might be expected, was attending the conference.
Which作主语时，谓语动词不限，主语被动皆可，只是谓语动词为
被动语态时助动词be省略。
2. as和which都可以在特殊定语从句中宾语。
3. as和 which在特殊定语从句中作补语。如：
We thought him a gentleman, as/which he could never be.
“as”特殊定语从句中可以主谓倒装，“which”从句中则不能主谓倒
装。
如果先行成分不是主语补语或宾语补语，关系代词用which而不用
as。如：
He talked like a native, which/as he hardly was.
4. which在特殊从定语句中作定语。
which可以在特殊定语从句中作定语，修饰fact, matter, thing 等名
词。这些名词代表先行成分表达的意义，有时将其略去句义仍然完整。
as不能作定语。如：
I was told to go not by train but bus, which advice I followed.
非限定性定语从句英语
非限定性定语从句英语定语从句有限制性和非限制性两种。
限制性定语从句是先行词不可缺少的部分，去掉它主句意思往往不明确；非限制性定语从句是先行词的附加说明，去掉了也不会影响主句的意思，它与主句之间通常用逗号分开，将非限定性定语从句放在句子中间，其前后都需要用逗号隔开。
中文名非限定性定语从句外文名non-restrictive/non-defining attributive clauses分类who引导Our guide，who was a French Canadian，was an excellent cook.我们的向导，一个法裔加拿大人，是一位优秀的厨师。
My gardener，who is very pessimistic，says that there will be no apples this year.我家的园丁非常悲观，他说今年将不结苹果。
whom引导关系代词whom用于指人，在句中作动词宾语和介词宾语，作介词宾语时，介词可位于句首。
如：Peter, whom you met in London, is now back in Paris.彼得现在回巴黎了，你在伦敦见过他。
Mr Smith，from whom I have learned a lot，is a famous scientist.史密斯先生是一位著名的科学家，我从他那儿学了许多东西。
whose引导whose是关系代词who的所有格形式，在从句中作定语。
whose通常指人，也可指动物或无生命的事物。
如：The boy, whose father is an engineer, studies very hard.这个男孩，他的爸爸是一位工程师，学习很努力Above the trees are the mountains, whose magnificence the river faithfully reflects on the surface.在树林的高处是山，其壮丽的景色完全映照在河面上。
非限制性定语从句
He wished to be such a man as Lei Feng was.
在the same …as结构中，as可以换成that， 但句意不一样。
This is the same book as I read last week.
这和我上周读的那本书是一样的。
This is the same book that I read last week.
他的妈妈很爱惜他,对他也很严格。
（2）先行词指人,在句中作宾语whom:
His wife, whom you met at my home, was a teacher.
他的妻子，就是你在我家遇见的那个，是一位老师。
（3）先行词指物,在句中作主语或宾语which:
Her house, which was built a hundred years ago, stood still in the earthquake. 那座房子在地震中依然耸立，它是一百多年 前建造的。 注意：无论先行词指人或者指物,在句中作 主语或者作宾语，非限制性定语从句的引 导词都不能用that。
（他还有其他的哥哥）
(2) 非限制性定语从句 His brother, who is now a doctor, always encourages him to go to college. 他的哥哥是当医生的，常鼓励他要考上大学。 （他只有一个哥哥）（“唯一”概念）
2、运用非限制性定语从句的情况
(非限制性定语从句中不用关系 词that/why；非限制性定语从句 中关系词不能省略)
Practice
1. The famous basketball star, who ___ comes from America, will visit our school soon. 2. In those days, she used to go to Mr black,with whom she had a wonderful _____ time.
非限制性定语从句
games and songs. 6. He is absorbed in work, ____he often was.
hometown，will open next year. 3. We shouldn’t spent our money testing so many people, most of
_____are healthy 4. Chan’s restaurant on Baker Street, ____used to be poorly run, is now
(2)Xi’an, which we visited last year, is really a beautiful city.
(3) My favorite season is autumn, when we celebrate the Mid-Autumn
Festival.
2. 在限制性定语从句中，作宾语的关系代词可以省略，但在非限制性 定语从句中，作宾语的关系代词不能省略。如：
(1)His father, who is a famous actor, will go to Canada next week.
(2)I was born in Beijing, which is the capital of China. 2. 当先行词被指示代词、形容词或物主代词修饰时，要用非限制性定 语从句。如：
练习： 1. His movies won several awards at the film festival, _____was beyond
非限定性定语从句
非限制性定语从句非限制性定语从句的作用是对所修饰的成分作进一步说明，通常是引导词和先行词之间用逗号隔开，将从句拿掉后其他部分仍可成立1. which引导的非限定性定语从句作用是说明前面整个句子的情况或主句的某一部分2.当先行词是专有名词、物主代词或指示代词所修饰时，其后的定语从句通常是非限制性的，例如：Charles Smith, who was my former teacher, retired last year.查理·史密斯去年退休了，他曾经是我的老师。
My house, which I bought last year, has got a lovely garden.我去年买的的那幢房子带着个漂亮的花园。
This novel, which I have read three times, is very touching.这本小说很动人，我已经读了三遍。
3.非限定性定语从句可将整个主句作为先行词, 对其进行修饰, 这时从句谓语动词要用第三人称单数，例如：He seems not to have grasped what I meant, which greatly upsets me.他似乎没抓住我的意思，这使我心烦。
Liquid water changes to vapor, which is called evaporation. 液态水变为蒸汽，这就叫做蒸发。
4.有时as也可用作关系代词5. 在非限定性定语从句中，不能用关系副词why和关系代词that，而用who, whom代表人，用which,whose代表事物，如果需要用why，可用for which代替.；p.s: which引导的非限制性定语从句其后不可省略成分，as可以关系代词引导的定语从句who指人在从句中做主语(1) The boys who are playing football are from Class One. 在踢足球的男孩们是一班的.(2) Yesterday I helped an old man who lost his way. 昨天，我帮助了一个迷路的老人.whom指人,定语从句中充当宾语，常省略。
非限定性定语从句讲解
A 引导非限定性定语从句的关系代词：B 引导非限定性定语从句的关系副词主要有：when,where使用规则及注意事项1. which引导的非限定性定语从句是用来说明前面整个句子的情况或主句的某一部分。
2. 在引导限定性定语从句时，that有时相当于in which, for which或at which 。
其中，介词的选用，依据从句中的动词所需搭配的介词来选用。
例句：①Attitudes towards daydreaming are changing much in the same way that(in which) attitudes towards night dreaming have changed.人们对白日做梦的态度正在改变，这与人们对夜间做梦的看法的变化有非常相似之处。
②I like the music for the very reason that(f or which) he dislike it.我出于某种原因喜欢这种音乐，而他恰恰与我相反。
③We arrived the day that(on which) they left.刚好我们到的那天他们走了。
3. as有时也可用作关系代词。
as引导非限制性定语从句，若as在从句中作主语，其引导的句子可以放在句首，也可以放在句中。
但which引导的非限制性定语从句只能放句中。
例句：As is reported in the newspaper ，some artistic treasures will be on show at the exhibition on the weekend.4. 在非限定性定语从句中，关系词不能用that。
限定性定语从句与非限定性定语从句的区别1.限定性定语从句: 从句不能省略,如果省略整个句子意思不完整。
非限定性定语从句: 从句可以省略,如果省略整个句子意思仍然完整。
2.限定性定语从句: 先行词可以用that 引导。
高中英语三大从句 串讲 教案
一. 定语从句1.重点突破(1)关系代词as的用法1)as可以引导限制性/非限制性定语从句，指人，物，事such+名词+as…像……一样（之类的）the same+名词+ as… 和…同…一样的2)as引导非限制性定语从句放在主句前，主句后，主句中as有“正如”之意，多用于肯定句典型例题讲解1In 2014, such important reform policies associated with the interests of the general public were introduced in China _____ almost each person could benefit from in life.A. whenB. thatC. whereD. as典型例题讲解2He works hard from dawn to night every day to make a living, _____many people who are struggling to survive in this big modern city.A. as ifB. such asC. so doD. as do(2)介词+关系代词的用法介词的选择主要考察以下几点：1)介词与先行词的搭配典型例题讲解Human facial expressions differ from those of animals in the degree _____they canbe controlled on purpose.A with whichB to which C. of which D. for which2)介词与从句谓语动词的搭配典型例题讲解1In the end, it was Becky ______ he turned for a gentle word and a smile.A. on whom B in whom C to whom D for whom典型例题讲解2Without facts, we can't form a worthwhile opinion for we need to have factual knowledge _____ our thinking.A which to base onB which to be based onC upon which to base D, with which to base on3)主从句逻辑关系典型例题讲解During the voyage the sailor caught a deadly disease ______ in those days medical science was helpless.A. that B which C. to which D. against which(3)关系副词When和where的用法1)when(指时间)=介词+ which,当先行词为指时间的名词时，关系词在从句中做时间状语积累：age (年代)；occasion (机会场合); interval (间隔); stay (逗留期间); stage (时间段)等抽象时间典型例题讲解She'll never forget her stay there _____ she found her son who had gone missing two years before.A. that B which C. where D. when2) where(指地点)=介词+which,当先行词为指地点的名词时，关系词在从句中做地点状语积累：job, situation., position, point, stage (舞台), case(情况), activity, atmosphere, email letter, process（流程）, compromise (和解妥协)等抽象地点名词典型例题讲解He wrote a letter _______ he explained what had happened in the accident.A. whenB. thatC. whichD. where2.难点(1)定语从句与强调句结合的用法典型例题讲解1--When was it that the exhibition was held?--It was on May 5 ______ the famous ancient Chinese poet Qu Yuan was honored.A. whenB. what C which D. that典型例题讲解2It is in the very village, ______ Mary was born 35 years ago, ______ she will build her first school, _______ inspires everyone to help her.A, where, that: which B. that: that: thatC. that; when; whichD. where: when; that2)定语从句与代词的用法典型例题讲解1Professor Smith is a strict but kind teacher, _______ is always trying to make his classes lively and interesting.A. the oneB. the one whoC. oneD. one who典型例题讲解2Have you read the book Life and Death Are Wearing Me Out by Mo Yan, ______ that won him the 2012 Nobel Prize in Literature?A. the oneB. oneC. thoseD. ones典型例题讲解3Mom promised to buy me a nice gift for my birthday, ______ beyond my imaginationA. the oneB. that C, which D. something典型例题讲解4Never should we forget the war and sufferings ______ c aused to the peopleA. itB. whichC. that D what(3)定语从句与同位语从句的用法1)被修饰词不同同位语从句的先行词通常是一些具有具体信息内容或者一定内涵的名词，比如idea, fact; hope, news, suggestion, proposal, word, thought, doubt. truth. possibility. order, promise而定语从句的先行词可以是名词代词，主句的一部分或者是整个主句.2)从句表达的含义不同定语从句是对其先行词的修饰或者限制，属于形容词性从句的范畴同位语从句是对前面抽象名词的进一步说明和解释，属于名词性从句的范畴3)引导词及其在句子中的成分不同有些引导词比如what, how, whether可以引同位语从句但是不能引导定语从句4)that引导的定语从句和同位语从句的区别引导词定语从句时在从句中做主语或者宾语，指物的时候可以用which代替，并且作语时常省路，在同位语从句中仅仅起到连接作用，不充当任何成分，并且不能省路，也不能用which代替典型例题讲解1Even if there is no scientific proof yet ______ secondhand smoke causes cancer, there is no reason why nonsmokers should be forced to take this risk.A. whichB. that C when D where典型例题讲解2I do n’t know the reason ______ you were absent from the meeting, but I am sure that someone will tell me the reason ______ you haven't told me.A. why, that B that: why C. because: which D. of which: that 典型例题讲解3After the earthquake, the relatives of children protected them from the knowledge ______ their parents already passed away.A. whenB. that C where D which(4)定语从句与非谓语结合的用法典型例题讲解1An explosion broke out in Hongdong county, Shanxi Province the other day, causing many miners injured, ______ to hospital immediately.A. most of whom sentB. most of them are sentC. most of them were sentD. most of them sent典型例题讲解2When asked what they would volunteer to do, ______ said they were willing to do something they could.A. half of theseB. half of whomC. half of whichD. half of them(5)定语从句与倒装结合的用法I'm going to spend the summer vacation in Shanghai, ______ lives my grandmother and some other close relatives.A. which B when C that D where3.易错点(1)定语从句中的插入语典型例题讲解1Newly released data point to an increase in technology use among children _____ some worry is changing the very nature of childhood.A. why B which C who D where典型例题讲解2--How are things going, Janet?--They have set out to deal with the present situation _____ they think deserves their immediate attention.A. which B where C. when D. what(2)定语从句中the way作先行词时，且关系词在从句中作状语，关系词可以用that, in which或者不填（/）型例题讲解_______, the young girl laughs the way _______ her mother did at that age.A. To my disappointment: thatB. To my joy; in whichC. To my surprise; /D. To my excitement; which(3)定语从句中先行词的识别典型例题讲解I came across a strange pers on near the cinema the other day, ______ there wasa talent show going on then.A. thatB. whenC. which D where(4)其他典型例题讲解1The zoologist hid himself among the bushes, _______ he could watch how the lions lived on the Grassland.A. whereB. which C from where D from which典型例题讲解2The reform and opening-up started in 1978, _______ the whole of China has witnessed great changes in almost every field.A. since whenB. WhenC. during whichD. since then典型例题讲解3He's a very good actor, _______ a lot of comedians are not, and he's a good director and a good writer as well.A. whoB. whereC. whom D which二. 名词性从句1.重点突破(1)连接词what和how的用法1)how(ever)+形容词+主语+系动词No matter how/However handsome you are, you can't commit a crime.2)how(ever)+副词+主语+谓语No matter how/However fast he runs, he can't get away.3) what(ever)+(a/an)+adj+名词+主语+系动词Whatever difficulties she met, she never gave up.典型例题讲解1Parents are taught to understand_____ important education is to their children's future.A. that B how C. such D. so典型例题讲解2-It seems that he was succeeded at last in the USA.-But you can never imagine______.A. what a hard life he has experiencedB. what he has experienced a hard lifeC. he has experienced what a hard lifeD. what a hard life has he experienced(2)what引导的特殊疑问句的回答典型例题讲解1-What are you anxious about?-____________.A. Whether we can succeed B If we succeedC Do we succeed D. That we can succeed典型例题讲解2-_______ made her ashamed of herself?-_______ the lowest mark in her class.A What: Because she got B. Was it that: GettingC. What was it that; That she gotD. What was it that: Get(3)as/ what/that句型辨析典型例题讲解1_______ is well- known to us is that consumers will buy goods if they think the price is reasonable.A. AsB. WhatC. ItD. That典型例题讲解2It is said ______ _______ was all ______ he said.A that; that, thatB what: what: whatC that, which: what D. that: that: which(4) wh-ever 与no matter wh-Wh-ever可以导名词性从句和让步状语从句，但no matter wh-只能引导让止步状语从句，因此，wh-ever.典型例题讲解1No matter _______ difficult problems we meet with, we will try our best to get them over.A howB what C. whatever D however典型例题讲解2-______ David says sounds right to Helen.-That's why she has made up her mind to leave with him ______ happens.A Whatever: whatever B. No matter what: whateverC. No matter what: No matter whatD. Whatever: however2.难点(1)名词性从句和强调句的结合典型例题讲解When asked to explain ______ he did to make his students so fascinated with his lessons, the teacher paused and thought deeply.A. what was it that B that what it wasC, what it was that D. what was it3.易错点(1)连接词what的特殊用法典型例题讲解She is ______ is known as a nosy person—she is always dying to know what's goingon in others' lives.A. whatB. whoC. whomD. that(2)连接词where的特殊用法典型例题讲解1You are saving that everyone should be equal, and this is _______ I disagree.A. whyB. where C what D how典型例题讲解2When you feel alone, just look at the spaces between your fingers, and remember that’s ______ my fingers fit perfectly.A. whatB. whereC. whyD. how三. 状语从句1.重点突破(1)连词when的用法典型例题讲解1Why did you go to work on foot on such a rainy day ______ you have a car of your own?A. whenB. whileC. as D, although典型例题讲解2The trouble with the global warming debate is that it has become a moral problem ______ i t's really an engineering one.A. untilB. becauseC. whenD. where典型例题讲解3Our mothers sat us down to read and paint, ______ all we really wanted to do was to make a mess.A. sinceB. asC. unless D when(2)连词while的用法while导让步状语从句，放在句首,译为“虽然”doing当如while用作时间连词时，意思相当于during that time(在……期间)表示某“段时间内发生的动作(while +doing )。
50第四章 非限制性定语从句
第四章 | 非限制性定语从句，今天这篇文章是要教大家顿悟非限定性定语从句。
非限定性定语从句也是一大考点和难点，今天我们会为大家做详细的讲解，内容较多，望同学们理清条理。
语法名词：非限定性定语从句与限定性定语从句的区别、非限定性定语从句的引导词which，who/whom/whose, as, when, where核心讲解：一、非限定性定语从句与限定性定语从句的区别非限定性定语从句是对先行词的一种附加说明，用逗号和主句隔开，最常见的形式就是“…, which…”。
既然加了“,”就说明和不加“，”的限定性定语从句有很大区别。
我们先来看一个例子：1. Freedom of expression, which is the most holy human right, is protected by the law.言论自由，（也就是）最为神圣的人权，受到了法律的保护。
句子中which指代主语freedom of expression，翻译成“（也就是）最为神圣的人权”。
如果按照普通的限定性定语从句翻译成“的”，反倒别扭：是最神圣的人权的言论自由受到了法律的保护。
所以，非限定性定语从句是对前面名词的“解释说明”，理解为“也就是”更为贴切；而限定性定语从句是对前面的名词进行“修饰限定”，理解为“的”。
二、非限定性定语从句的两种指代对象非限定性定语从句的另一个难点是which到底指代谁？以前英语老师强调过“既可以指代前面的名词，又可以指代前面整个一句话”。
如何判断呢？我们再来看个例子：2. He missed the train, which made him angry.他错过了这趟火车，而这使他很生气。
这里的which指代火车还是整个主句呢？如果把火车代入到定语从句当中去，“火车使他很生气”，意思讲不通！而把整个主句代入到定语从句当中可以表示“（他错过了这趟火车）这件事使他很生气”，完全讲得通。
所以，判断which到底指代名词还是整句的方法很简单：把名词和整句分别代入到定语从句中，哪个意思讲得通，which就指代哪个。
初中英语--as引导的从句省略有没有规则,as引导定语从句语法归纳
as引导的从句省略有没有规则,as引导定语从句语法归纳as...as引导比较状语从句的省略问题1. I read as many pages as are required.这句中没有省略，其中的 as 是关系代词，引导定语从句（as are required）。
句意为：要求读多少页我就读多少页。
2. The girl are as busy with their work as bees.原句有笔误，girs 应为 girls。
此句可认为 bees 之省略了系动词 are。
as…as 结构的基本用法，句意为：姑娘们的工作十分忙。
注意句中的 as busy as bees 为习语，意思是“非常忙”。
3. Work is as necessary for peace of mind as for health of body.此句若要说有所省略，可认为是Work is as necessary for peace of mind as it is necessary for health of body 的省略，其意为：工作不仅对于心灵的平静是必要的，对于身体的健康也是必要的。
4. Buying a new bike is sometimes as cheap as repairing the old one is.不知你的句子出处何处。
感觉句末的 is 是多余的。
句子大意为：买一辆新的自行车有时跟修理旧自行车一样便宜。
as引导定语从句语法归纳（一）as(代词)引导限制性定语从句1. 当先行词是“such/the same+名词”时，用as引导定语从句。
即，such+n.+as(代词)，the same +n.+as(代词)。
例句（as指代such+n.，作主语/宾语/表语）●We invited all such people as were likely to come.（as在从句中作主语。
非限制性定语从句
4. (09宁夏)She brought with her three friends, none of ____ I had ever met before. A. them B. who C. whom D. these 答案：C 解析：考查定语从句中的非限制性定语从句。句意为： 她带着她的三个朋友，他们三个中没有一个人我曾见过。
例2.（2012，陕西）It is the third time that she has won the race,____ has surprised us all. A. that B. where C. which D. what
解析：根据非限制性定语从句的定义可以首先排除A选 项，B选项主要指地点，D选项不用做定语从句的连接， 因此此题 Nhomakorabea案为选项C。
实战提高
1.（10四川）After graduating from college，I took some time off to go travelling， ______ turned out to be a wise decision． A．that B．which C．when D．where 答案：B 考点：考查定语从句。 解析：此处应为which引导的非限制性定语从句，which 代替前边整个句子。句意为：“大学毕业后，我休假一 段时间去旅游，这结果证明是一个明智的决定。”
as引导非限制性定语从句，从句的位置多变，形 式灵活，但其有相对固定的搭配，可以帮助我们快速、 准确地做出选择： as anybody can see as is well known as we expected as often happens as is mentioned above as has been said before 此时，as可以译做“就像……一样”。 比如： As is known to all, the moon travels round the earth.
非限制性定语从句的引导词通用3篇
非限制性定语从句的引导词通用3篇非限制性定语从句的引导词 1一.非限制性定语从句的定义：非限制性定语从句和主句的关系不是十分密切，只是对先行词或主句作些附加说明，如果去掉，主句的意思仍然完整。
这种从句和主句之间往往用逗号隔开。
引导非限制性定语从句的关系词与引导限制性定语从句的关系词略不同。
除了that和why不能引导非限制性定语从句之外，其他的都可以。
例如：He is English,which I know from his accent.他是英国人，那是我通过他的口音知道的。
（该句的主句为“He is English”→“他是英国人”；从句为“Which I know from his accent”→“我从他的口音得知的”，如果把从句去掉，句子就剩下He is English,也不影响读者知道他是个英国人。
该句中的从句只是补充说明从口音推断他是个英国人的,属于非限制性定语从句，且习惯用逗号隔开。
）二.非限制性定语从句的引导词：非限制性定语从句的关系代词无论指人还是指物，都不能用that。
指人时，如果关系代词在从句中作主语，就用who；做宾语时就用whom。
指物时要用which。
这里要注意的是，关系代词在非限制性定语从句作做宾语时也不能省略。
例如：Jim,who is from China, has a good mand of English.吉米来自__，他精通英语。
Jim,whom you met in China, is now back in Paris.吉米现在回巴黎了，你在__见过他。
（该句属于非限制性定语从句。
从句中的whom指人，在从句中作宾语，原句为you met him in China,him指代的就是Jim，且him在从句中作宾语。
从句也是把主句分开了，用逗号把其主句隔开。
）The puter,which his father bought for him yeaterday, is helpful for him.他爸爸昨天给他买了台电脑，它对他来说很有用。