限制性定语从句与非限制性定语从句的含义

限制性定语从句是先行词在意义上不可缺少的定语,若去掉,所修饰主句的内容就不完整或失去意义.这种从句和主句的关系十分密切,写时不可用逗号分开. 在复合句中充当同位语的名词性从句称为同位语从句.
what, how, if, whatever 等可引导同位语从句,但不引导定语从句.that引导同位语从句时,它不充当句子成分,而引导定语从句时,它作为关系代词,要么充当定语从句的主语,要么充当定语从句的宾语.如上例 that he told us中的that就充当told的宾语.同位语从句所修饰的名词比较有限,通常有hope, wish, idea, news, fact, promise, opinion, suggestion, truth等,而定语从句所修饰的名词则非常广泛. 另外,when和where 引导定语从句时,通常只修饰表示时间和地点的名词,而它们引导同位语从句时却不一定；又如why引导定语从句,它通常只修饰名词the reason,而它引导同位语从句时则不一定

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,例如：
This is the house which we bought last month.这是我们上个月买的那幢房子.（限制性）
The house,which we bought last month,is very nice.这幢房子很漂亮,是我们上个月买的.（非限制性）
2) 当先行词是专有名词或物主代词和指示代词所修饰时,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) 非限制性定语从句还能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.
说明：关系代词that和关系副词why不能引导非限制性定语从句.

引导非限制性定语从句时与which的区别
①当主句和从句语义一致时,用as；反之,用which来引导非限制性定语从句.e.g.He made along speech,as we expected.
He made along speech,which was unexpected.
②当非限制定语从句为否定时,常用which引导.
e.g.Tom drinks a lot everyday,which his wife doesn’t like at all.
2.关系代词在从句中作主语时,从句的谓语动词单数还是用复数应由先行词决定.e.g.The man who lives downstairs speaks English fluently.住在楼下的那个人英语说得很流利.The students who are in GradeThree are going to climb the hill tomorrow.
3.定语从句有时不直接紧靠先行词,中间由一个定语、状语或谓语隔开.e.g.There is an expression in his eyes that I can’t understand.
4.引导定语从句的关系副词有时可以用“介词+which”来代替.
e.g.October 1,1949 was the day on which(=when)the People’s Republic of China was founded.
5.当定语从句中谓语动词是带介词或副词的固定短语动词时,短语动词的各个固定部分不要拆开.
e.g.The sick man whom she is looking after is her father.
6.介词在关系代词前,只能用which和whom,且不能省略；介词在句尾,关系代词可有which,that,whom,口语中也可用who,且可省略.
e.g.The man(whom/who/that)you were talking about has come to school.

限定性定从的理解在于你理解who whose whom who which 这些词.你说的要看情况
who指人,在定从里做主语,which指物定从做主语,whom指人做宾语,whose指人指物,做主语.举个例子:whose son won the game
the son of his won the game .个人认为是第二种,但是不用纠结于whose + noun 是等到同于 of which/whom +the+n 还是等同于the +n +of +which/whom.因为当你真正理解定从后就不会这样了

区别其实很简单.
以你的例句为例.
“Thai families which live together in the same house are large.”
“Thai families”是定语从句修饰的先行词,“which live together in the same house”是定语从句.
剩下的是句子的谓语部分.
区别方法：1.去掉定语从句
句子变为“Thai families are large.”
2.看这个句子能否表达出清晰的含义.
很明显,这个“Thai families ”凭空出现,指代不明,必须得对其进行修饰,才能让人明白,这便是限制性定语从句.
限制性定语从句与先行词紧密相关,不能删去.所删去,主句意义表达不清.
若删去后,句子仍能表达出清晰含义,则说明先行词可以不需要被定语从句修饰.这样的即为非限制性定语从句.
对于你举的两个例句,是你自己想出来的吧,不怎么恰当..恩,好好再看看吧,不要昏了.

who are in trouble

Good question.
以我的理解是,一般要紧跟先行词.
我参看了《实用英语语法》一书的定语从句一章,还真没看到你这种用法将从句放在birthday的.
不过,你这个句子如果把which was a wonderful book放在末尾,倒是很像一个非限制性定语从句.因为如果去掉它不会影响句子含义.注意判断是限制性还是非限制性不能只看逗号的.

非限定性定语从句起补充说明作用,缺少也不会影响全句的理解,在非限定性定语从句的前面往往有逗号隔开,如若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...

在定语从句中,关系代词that ,which,whom 在定语从句中作宾语宾语时可以省略,例如
He found the book ( which/that ) he lost yesterday.
This is the boy (whom ) I talked of the other day.
如果定语从句中出现把从句中的介词提前到关系代词which和whom 之前,这时候关系代词which和whom 作介词宾语时,关系代词不能省,介词提前关系词不能用that .
This is the pen ( which /that) he wrote his composition with.在这个句子中which/that可省.
This is the pen with which he wrote his composition.这个句子中 which 就不能省.
I like the boy (whom ) we played football with.
I like the boy with whom we played football .

非限定性定语从句起补充说明作用,缺少也不会影响全句的理解,在非限定性定语从句的前面往往有逗号隔开,如若将非限定性定语从句放在句子中间,起前后都需要用逗号隔开.
①引导非限定性定语从句的关系代词：
指代对象 指代人 指代物
主格 who which,as
宾格 whom which,as
所有格 of whom,whose which,of which,whose
②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 in much 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(for 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 .
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.
非限定性定语从句:先行词不可以用that 引导.
3.限定性定语从句:引导词有时可以省略.
非限定性定语从句:引导词不可以省略.
4.限定性定语从句:主句与从句不需要用逗号隔开.
非限定性定语从句:主句与从句需要用逗号隔开.
5.限定性定语从句:从句只修饰先行词.
非限定性定语从句:从句即可以修饰先行词,也可以修饰整个句子或句子的一部分.
功能和形式方面的区别
限定性定语从句与主句的关系很紧凑,对其先行词起限定、修饰的作用.如果将其去掉,会影响句子意思的完整性；有时甚至于引起费解、误解.例如：
1.Rainforests are being cleared for valuable timber and other resources to speed up the economic growth of the nationsin which they are located .为了加速他们各自所在国家的经济发展,热带雨林作为有价值的原木和其他资源正为人们所砍伐.
2.Ocean currents affect the climates of the lands near which they flow.洋流影响其流经的附近地区的气候.
3.They explained the reason to us why they had hated us before.他们向我们解释为什么他们不喜欢我们的原因.
非限定性定语从句在形式上就与主句很松散,它与主句之间有一个逗点","隔开；它对其先行词没有限定、修饰的作用,只起补充、说明的作用.有时也用它来对全句或句中某个成分进行补充、说明.即使将其去掉,也不会影响句子意思.由于上述原因,非限定性定语从句在表达意思方面也有别于限定性定语从句.另外,非限定性定语从句在中文译文里,我们往往将其作为一个分句处理,而不把它作定语翻译.例如：
Earlier ,the Babylonians had attempted to map the world ,but they presented it in the form of a flattened disc rather than a sphere ,which was the form adopted by Ptolemy .更早之前,巴比伦人曾试图绘制世界地图,但是他们把它绘制成平盘状而不是托勒密所采用的球体状.（此句中,非限定性定语从句是对先行词a sphere进行补充、说明.）
The combination of satellites,which transmit information ,computers ,which store information ,and television ,which displays information ,will change every home into an education and entertainment center .卫星能传输信息,计算机能储存信息,电视能显示信息,把这些手段结合起来可以使每个家庭都成为教育娱乐的中心.（此句中,三个非限定性定语从句分别对三个先行词：satellites ,computers和television进行补充、说明.如果去掉这三个非限定性定语从句,那么句子可简化为：The combination of satellites ,computers and television will change every home into an education and entertainment center .）
The sun heats the earth ,which makes it possible for plants to grow .太阳给予大地热,这就使植物的生长成为可能.（此句中,非限定性定语从句是对全句进行补充、说明,将全句表达的意思看成"一件事情）.
The old man has a son ,who is in the army .那位老人有一个儿子,他在部队工作.（此句中,非限定性定语从句是对先行词son进行补充、说明.但本句所传达的信息是："这位老人只有一个儿子" .如果将此句改写成限定性定语从句："The old man has a son who is in the army .”那位老人有一个在部队工作的儿子.那么,限定性定语从句就要对先行词son进行限定、修饰.这样一来,句子所传达的信息就变成了："这位老人有一个儿子在部队工作",也就是说可能老人还有其他的儿子在干别的工作）

1.指人：who,whom,that
Is he the man who/that wants to see you?(who/that在句中作主语,不能省略.）
He is the man (whom/that) I saw yesterday.(whom/that在从句中作宾语,可以省略.）
2.指物：which,that
The bank which/that was opened last week is a modern one.(which/that在句中作主语,不能省略.)
The briefcase (which/that) you are carrying is heavy.(which/that在从句中作宾语,可以省略.)
3.所有格：whose (指物时可以同of which互换,指人和of whom 互换)
They rushed over to help the man whose car （the car of whom)had broken down.
Please pass me the book whose cover(of which the cover/the cover of which) is green.
注：根据句子意思和结构需要,必须使用适当的介词.介词后关系词不能省;介词后不能用that:
Do you know the boy (whom/that) I talked to just now?
=Do you know the boy to whom I talked just now?
The palace to which I often pay a visit was built in the 17th century.
Yesterday I bought a pen with which I can write my composition.
关系副词：when,where,why (相当于“介词＋which”结构）
1.when 在从句中作时间状语
I still remembered the day (that/which) we first met on.(正)
I still remembered the day on that we first met.(误)
I still remembered the day on which/ when we met.(正)
比较：I still remember the day (that/which) we spent together.
2.where在定语从句中作地点状语
Shanghai is the place where /in which I was born.
Shanghai is the place (which/that) I was born in.
比较：Shanghai is the place (which/that) I visited last year.
3.Why在定语从句中作原因状语
Is this the reason why /for which he refused our offer?
比较：This is the reason (that/which) I gave to my teacher.
所以：判断使用关系代词或关系副词不能光看先行词是否是表示时间,地点,原因的名词,必须分析从句谓语动词与先行词的逻辑关系.如果关系词在从句中作状语则分别用when,where或why 等关系副词；如作主语或宾语,则仍用关系代词which或that.

从表面看,限制性定语从句和主句之间没有“,”逗号.
非限制性定语从句 有 “,”
从功能上看,限制性定语从句 对先行词 进行识别 筛选.
非限制性定语从句 补充说明.
比如His brother who joined the army has returned home.
限制性定语从句who joined the army 对brother进行识别,筛选,他参军的那个兄弟.
言外之意是,他有2个或以上兄弟.
His brother,who joined the army has returned home.
非限制性定语从句,对his brother 补充说明,他的兄弟,之前参军去了,现在回来了.
言外之意,他只有一个兄弟.

限制性定语从句要翻译到先行词前面,翻译成“...的”.
比如：I know the man (who is watching us.)
翻译成：我认识(那个正在看我们的)人.
非限制性定语从句要单独翻译成一句话.
比如：He lives in Shanxi,(which is only about an hour's ride from here).
翻译成：他住在陕西,离这里至于一个小时的车程.
这些都是书面解释,语言的应用上还需要多多琢磨,不是一成不变的.

作表语：
e.g.I have got into the same trouble as he has.
作主语：
e.g.John does not have as many English books as Tom does.

这个which做宾语指的是做后面bought的宾语.

区别是限制性定语 从句的主句和从句之间没有符号间隔,非限制性定语从句的从句的主句和从句之间有符号间隔.限制性定语从句可用关系词which,that,what,as非限制性定语从句用which

算错.
限定性从句的先行项,也就是定语从句所修饰的人或事物是不确定的；而非限定定语从句的先行项所修饰的人或事物是确定的.
例如,我想表达“这就是他的父亲,一个普通的工人”,必须用非限定定语从句来翻译：This is his father,who is an ordinary worker.
如果用限定性定语从句：This is his father who is an ordinary worker.意思就变成了“这是他身份是普通工人的父亲”,言外之意也就是说,他有好几个父亲,这个父亲是其中之一,身份是普通工人.这样一来意思和原句就大相径庭了.

不对1 关系代词在从句中做介词的宾语,介词常提前,但介词提前时,关系代词只用用which whom the school in which he once studied in is very famous
we will go to hear the famous singer about whom we have often talked about2 关系副词 when where why 和介词+which 之间的关系 关系副词 when where why 可以适当用介词+which 来替代.
如 i won't forget the date when(on which) i was born

最直观的说：非限定性定从最明显的标志就是有“,”与主句或先行词隔开.
其次,
非限定性定从是不能由that引导的
最后,
非限定性定从和限定性定从的意义上区别：
限定性定从删去后,句子明显不完整或很突兀,有时就像病句
eg.He is a person who never gives up.
=>He is a person.(“他是个人”这样的句子不是很奇怪吗?)
----------------------------
而非限定性定从就对主句起到一个补充说明的作用：
I found him in the woods,where has a well-known tree.
(我是在树林里找到他的,那里有一棵很有名的树.)

①引导非限定性定语从句的关系代词：　　指代对象 指代人 指代物
主格 who 、 which,as
宾格 whom 、which,as
所有格 of whom whose 、whose which,of which,②引导非限定性定语从句的关系副词主要有：when,where

and but so 都是一个句子.and but so 是用来连接句子的上下部分.and 是承接 But是转折 so是结果.

用that
those后面可以用that

这是一定的哦含义上,前者是对先行词的补充说明,是不必要的,也就是说,如果去掉非限定从,原句的句意仍然成立；后者是先行词的必要修饰,如果去掉则原句不完整.
形式上,前者在先行词和从句之间加逗号,后者不加.
例如：
限制性定从：There is somebody who wants to speak to you.（若去掉从句,则变为：There is somebody.句意不完整.）
非限定从：My house, which I bought last year, has got a lovely garden.（若去掉从句,原句依旧成立.）

非限制性定语从句是用来对名词或代词进行补充说明的,而限制性定语从句是对名词或代词的内容进行限定,即一定/或只要满足定语从句所说的条件才行.也就是说限制性的范围比非限制性的大.就用你的句子为例：
My best friend,I see every day,is a great sport fan.I see every day 是对我的好朋友的补充说明.如果改成限制性的,就变成了“我天天看到的好朋友”,而不是隔几天看到的,即强调一定是要天天看到的那个才是你说的人.很显然,在这个句子里是不需要强调这个方面的.
第二句,如果改成限制性的,那就变成了限定条件,即一定是跟你住一幢楼里的zhenhui,那说明还有其他的zhenhui.
再如：
The girl whose father is the headmaster is my classmate.这个句子是说只要爸爸是校长的女生都跟我是同学.很显然,这是荒谬的.如果改成非限制性,就合理了,即对这个女生进行解释说明,而不是限定.

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.
引导定语从句的关系代词有：that（指人或物）,which（指物）,who (指人）.指人时可用that或who ；指物时可用that 或which ；但有时只能用that,不能用which.常见的情况有下列五种：
1） 当先行词是：all , any , anything , everything , nothing或被它们修饰时.例如：
Is there anything that I can do for you ?
有什么可以为你做的吗?
All that can be done must be done .
凡是能做的都必须做.
2）当先行词被形容词的最高级或序数词修饰时.例如：
That is one of the most interesting books that are sold in the bookshop .
那是这家书店出售的最有趣的书之一.
The first thing that we should do is to get some food .
我们该做的第一件事是弄点吃的.
3）当先行词有：the only , the very , the same , the last 等修饰时.例如：
My necklace is not the only thing that's missing .
我的项链不仅是丢掉的东西.
4）当主句以who或which开头时,定语从句中引导词用that ,不用which 或 who .以避免重复.例如：
Who is the girl that is wearing a red coat ?
正穿一件红色外套的女孩子是谁?
5）当先行词既有人又有物时,用that .例如：
The writer and his novel that you have just talked about are really well known .
你刚才谈起的那位作家以及他的小说确实很著名.

we should make good use of time which is so precious .
限制性定语从句不用逗号与主句分开,对所修饰的词起特指或限定的作用,去掉后意思不完整或不太清楚.翻译成中文时,一般把定语从句翻译在先行词之前.
非限制性的定语从句和主句之间往往用逗号分开,只对被修饰的词语或主句起补充说明的作用,去掉后对句意影响不大.翻译时通常把定语从句翻译在先行词后边,作为附加说明.

通常不能,因为限制性定语从句相当于先行词的定语,即限定先行词的性质、程度或范围,而非限制性定语从句却通常是对先行词进行补充或附加说明,即使即使去掉,对主句的影响也不太大.

限制性和非限制性定语从句
1) 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,例如：
This is the house which we bought last month.这是我们上个月买的那幢房子.（限制性）
The house,which we bought last month,is very nice.这幢房子很漂亮,是我们上个月买的.（非限制性）
2) 当先行词是专有名词或物主代词和指示代词所修饰时,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) 非限制性定语从句还能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.
说明：关系代词that和关系副词why不能引导非限制性定语从句.

限定性定语从句是句中不可缺少的组成部分,主从句之间不能用逗号隔开,翻译时常放在被修饰词的前面；非限定性定语从句则用逗号与主句分开,且不加时并不影响主句的意思.只是对先行词作附加说明.而且非限定性从句一般不用that 引导如：
My brother who/that lives in New York has four children.我住在纽约的那个哥哥有四个.（限定性定语从句,可能还有其他的哥哥.）
My brother,who lives in New York ,has four children.我哥哥有四个孩子,他住在纽约.

限制性定语从句,which前面没有逗号
非限which前面有逗号.
如果非要从理解入手,那么限制性定语从句,which后面的内容对于前面的先行词来说,是不可缺少的,如果少了which后面的内容,句子就不成立,没有逻辑
而非限,which后面的内容只是对前面先行词的补充说明,删掉也不影响整个句子的逻辑完整性

最简单的区别就是限制性的从句和主句之间通常没有逗号,而非限制性定语从句有.
非限制性定从通常不用that引导 主要引导词有which where
非限制性定从通常翻译时可单独成句 和主句的 联系没有限制性定从强
具体的 区别你需要 自己查查参考资料
加深印象

限制性定语从句与非限制性定语从句的区别如下：
一、在书写形式上,限制性定语从句紧接着主句写,非限制性定语从句和主句隔开.
He is a man who has won six medals.
He is a man,who has won six medals.
二、限制性定语从句对先行词有限制修饰的作用,使得先行词具有区分于其它同类事物的特点.
It is the tree I planted three years ago.
这是我三年前栽种的那颗树（不是其它的树）.
而非限制性定语从句并没有上述作用,相反,它是对先行词起补充说明的作用.
It is a tree,which I planted three years ago.
这是一颗树,我三年前栽种的（补充说明树栽种的时间）.
三,限制性定语从句对先行词具有限定性,非限制性定语从句体现先行词的唯一性.
John likes his father who has studied abroad.约翰喜欢他出国学习过的那个父亲（给人感觉他另外还有其它没出国过的父亲）
John likes his father,who has studied abroad.约翰喜欢他的父亲,他父亲出国学习过.（约翰的父亲是唯一的）
四,语法区别.常考的一点是：非限制性定语从句修饰物,关系代词只能使用which,不能用that.
It is a tree,which I planted three years ago.
It is a tree,that I planted three years ago.(错)

as 可以用作关系代词,在限制性定语从句中 ,多同such 或the same 连用,构成 such.as
和 the same...as结构 .as 的先行词可以是人或物.如
he is not such a fool as he looks.他貌似憨傻 实则不然.
the same ...as 表示同一类的 如 this is the same book as i bought yesterday.
the same...that 表示同一个 如 this is the same book that i am looking for.
不过 有时区别不大 可以互换
如 we drove out of the town by the same road as/that we had entered by.
我们从进城的原路开车出城去.

不可以.可以用介词加which、that

在复合句中用作同位语的从句叫同位语从句.它一般跟在某些名词后面,用以说明该名词表示的具体内容.This is because they come from a computer program called ICQ,which means I seek you.这句中是非限定性定语从句,因为第一,根据第二条,它构不成主系表结构,第二,从句起修饰的作用 定语从句与同位语从句在形式以及它们在句中的位置上都很相似,但它们在句中的句法功能不同,所用的引导词也不完全一样.1.定语从句是形容词从句,其句法功能相当于一个形容词,与前面的名词是修饰与被修饰关系,即限定它前面的名词范围,或补充一些情况；而同位语从句是名词性从句,其作用相当于一个名词,与前面的名词是同位关系,是对前面的名词作进一步解释,即说明它前面名词的内容.如：The news that he told me just now is true.他刚才告诉我的消息是真的.（定语从句） The news that I have passed the exam is true.我通过了考试这一消息是真的.（同位语从句） 2.同位语从句与其所修饰的名词之间是一种同位关系,二者之间存在逻辑上的系表关系,可用“主系表”结构来表示,而定语从句则没有这种关系.如：The news that he won the first place is true.他赢得冠军的消息是真的.（同位语从句） 若用“主系表”结构来表示,则是：The news is that he won the first place.那个消息是他赢得了冠军.3.定语从句的先行词可以是各类名词,而可跟同位语从句的名词通常只是 news,idea,fact,promise,question,doubt,thought,hope,message,suggestion,possibility 等少数几个.因此,引导两种从句的连接词也不完全一样.可以引导定语从句的连接词有 that,which,who,whom,whose,when,where,why 等.可以引导同位从句的连接词有 that,whether,when,where,how 等.如：The factory which / that we visited yesterday is a chemical one.我们昨天参观的那家工厂是化工厂.（定语从句） I’ve come from Mr Wang with a message that he won’t be able to see you this afternoon.我从王先生那里得知一个消息,他今天下午不能来看你了.（同位语从句） 4.定语从句的引导词在从句中充当一定的成分,可作主语、宾语、状语等；而同位语从句中的引导词在从句中起连接作用,不作任何句子成分.如：The idea that he gave surprises many people.他提出的观点令许多人感到吃惊.（定语从句,that 在从句中作 gave 的宾语） The fact that they didn’t finish the work has to be faced.必须面对事实,他们没有完成工作.（同位语从句,that 在从句中只起连接作用,引导从句解释 fact 的内容,不作任何句子成分） 5.引导定语从句的连接词有时可以省去,而引导同位语从句的连接词则不可省去.如：I’ll keep the promise （that / which） I made two years ago.我将履行两年前许下的诺言.（定语从句） I make a promise that I will write to you as soon as I get to Beijing.我许诺,我一到北京就给你写信.（同位语从句） 6、若连词为特殊疑问词,根据从句是否有疑问的意义判断.如：eg.Do you remember the day when i told you that i loved you?(when引导的从句不表示疑问,所以这是一个定语从句.） eg.I have asked the question why it was true just now.(why引导的从句表示疑问,所以这是一个同位语从句.） 这些我也看不懂.

最直观的说：非限定性定从最明显的标志就是有“,”与主句或先行词隔开.
其次,
非限定性定从是不能由that引导的
最后,
非限定性定从和限定性定从的意义上区别：
限定性定从删去后,句子明显不完整或很突兀,有时就像病句
eg.He is a person who never gives up.
=>He is a person.(“他是个人”这样的句子不是很奇怪吗?)
----------------------------
而非限定性定从就对主句起到一个补充说明的作用：
I found him in the woods,where has a well-known tree.
(我是在树林里找到他的,那里有一棵很有名的树.)

最明显的区别就是限制性的从句和主句之间通常没有逗号,
而非限制性定语从句有.
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.

定语从句是由关系代词或关系副词引导的从句,其作用是作定语修饰主句的某个名词性成分,相当于形容词,所以又称为形容词性从句,一般紧跟在它所修饰的先行词后面.定语从句又分为限制性定语从句和非限制性定语从句.限制性定语从句对被修饰的先行词有限定制约作用,使该词的含义更具体,更明确.限制性定语从句不能被省略,否则句意就不完整.非限制性定语从句与先行词关系不十分密切,只是对其作一些附加说明,不起限定制约作用.如果将非限制性定语从句省去,主句的意义仍然完整.

something是不定代词,当先行词是不定代词时,决不能用其它的,就只能用that,something绝对不除外

这里后面的定语从句中成分已经全了,因此缺的是状语,而与case常连用的就是where了,表示在那个例子中
which当然可以引导限制性定语从句,但是前提是从句中有成分残缺
的确where是表示地点,但也可以表示抽象的地点,在例子里面就是个抽象的地点
其他的还有stage,situation,point等
这里的case不能解释为盒子

简单地说：
1、只要前面没介词,能用which的就能用that
2、如果句子中出现另外一个层次的从句,且出现了that 或which,那么,这个句子就要避免重复出现相同的,而用另一个
3、在从句中做逻辑主语（包括两种情况：一种是,实际主语就是that；第二种,虽然先行词that在引导的句子不是主语,但是是逻辑主语）时,只用that；做宾语时,尽量用which,同时,可用that替换

写个句子给你看,
你就懂了,
the man who is sitting over there is my father, 限制性定语从句,坐在那边的人是我的爸爸,言下之意,你有不止一个父亲,而你需要限制是坐在那边的那个父亲.
the man,who is sitting over there,is my father
而这个非限制定语从句,说明你只有一个父亲,不需要限定.

句中that引导的不是定语从句,而是同位语从句,作为主语it的同位语.
(形式主语It) (谓语is) (宾语a truth) (过去分词作定语universally acknowledged),(主语同位语从句that a single man in possession of a good fortune must be in want of a wife).
翻译：一个拥有很多财产的单身男人,肯定想要个太太,这是全世界都知道的真理.

限制性定从,介词后的关系代词不能省,即whom不能省
非限制性定从中,不论是否位于介词后,关系代词都不能省
标星号的句子whom是在定从中作宾语
初中遇到的定从多数为限制性定从

如果用英语定语从句来给你讲,你永远搞不清楚,因为你已经糊涂了,我只用两句中文例子表达一下,你一下就自然发现什么是限定什么是非限定了.
所谓定语从句,就是用句子做了形容语来修饰先行词,那这个句子叫定语从句.（基本是这样,特殊情况例外,先不讲,讲多你就晕了）
我有一个长着一头长发的女儿.（主：我 谓：有 宾：女儿 ）（长着一头长发的）=定语
我有一个女儿,她长着一头长发.
中文我想你一下就看明白了,第一句要表达的意思是完全清晰准确的,也就是说定语一定要修饰宾语这个名词的.
而第二句只是泛泛的说明了一下,没有强调.我有个女儿,他长着一头长发,靠,应该明白了吧!
英语的限定与非限定完全取决于中文你要表达的意思,对吧,你的中文严密,英语就限定,不严密强调,英语就非限定.
你肯定会问为什么要用句子来代替形容词,因为英语中没有这样的单词有这样的意思,你可以说一个漂亮的女孩,a beautiful agirl,你能找一个单词是这样的意思吗,长着一头长发的,因为没有一个单词是这样的意思,所有要用英语从句.
我有一个长着一头发长的女儿.限定
I have a girl who has long hair.
我有一个女儿,她有一头长发.非限定
I have a girl,who has long hair.
看明白了吗?关键是你想要表达什么,英语就是根据你的意思来写的.

这种问题不知怎么具体说明 只能找些限制性定语从句的例子你自己体会
定语从句（Attributive Clauses）在句中做定语,修饰一个名词或代词,被修饰的名词,词组或代词即先行词.定语从句通常出现在先行词之后,由关系词（关系代词或关系副词）引出.
关系代词有：who, whom, whose, that, which等.
关系副词有：when, where, why等.
关系代词所代替的先行词是人或物的名词或代词,并在句中充当主语、宾语、定语等成分.关系代词在定语从句中作主语时,从句谓语动词的人称和数要和先行词保持一致.
1）who, whom, that
这些词代替的先行词是人的名词或代词,在从句中所起作用如下：
Is he the man who/that wants to see you?
他就是你想见的人吗?（who/that在从句中作主语）
He is the man whom/ that I saw yesterday.
他就是我昨天见的那个人.（whom/that在从句中作宾语）
2) Whose 用来指人或物,(只用作定语, 若指物,它还可以同of which互换）, 例如：
They rushed over to help the man whose car had broken down. 那人车坏了,大家都跑过去帮忙.
Please pass me the book whose (of which) cover is green. 请递给我那本绿皮的书.
3）which, that
它们所代替的先行词是事物的名词或代词,在从句中可作主语、宾语等,例如：
A prosperity which / that had never been seen before appears in the countryside. 农村出现了前所未有的繁荣.（which / that在句中作主语）
The package (which / that) you are carrying is about to come unwrapped. 你拿的包快散了.(which / that在句中作宾语）
关系副词可代替的先行词是时间、地点或理由的名词,在从句中作状语.
1）when, where, why
关系副词when, where, why的含义相当于"介词+ which"结构,因此常常和"介词+ which"结构交替使用,例如：
There are occasions when (on which) one must yield. 任何人都有不得不屈服的时候.
Beijing is the place where (in which) I was born. 北京是我的出生地.
Is this the reason why (for which) he refused our offer? 这就是他拒绝我们帮助他的理由吗?
2）that代替关系副词
that可以用于表示时间、地点、方式、理由的名词后取代when, where, why和"介词+ which"引导的定语从句,在口语中that常被省略,例如：
His father died the year (that / when / in which) he was born. 他父亲在他出生那年逝世了.
He is unlikely to find the place (that / where / in which) he lived forty years ago. 他不大可能找到他四十年前居住过的地方.
·判断关系代词与关系副词
方法一： 用关系代词,还是关系副词完全取决于从句中的谓语动词.及物动词后面无宾语,就必须要求用关系代词；而不及物动词则要求用关系副词.例如：
This is the mountain village where I stayed last year.
I'll never forget the days when I worked together with you.
判断改错（注：先显示题,再显示答案,横线；用不同的颜色表示出.）
（错） This is the mountain village where I visited last year.
（错） I will never forget the days when I spent in the countryside.
（对） This is the mountain village (which) I visited last year.
（对） I'll never forget the days (which) I spent in the countryside.
习惯上总把表地点或时间的名词与关系副词 where, when联系在一起.此两题错在关系词的误用上.
方法二： 准确判断先行词在定语从句中的成分(主、谓、宾、定、状),也能正确选择出关系代词/关系副词.
例1. Is this museum ___ you visited a few days age?
A. where B. that C. on which D. the one
例2. Is this the museum ____ the exhibition was held.
A. where B. that C. on which D. the one
答案：例1 D,例2 A
例1变为肯定句： This museum is ___ you visited a few days ago.
例2变为肯定句： This is the museum ___ the exhibition was held.
在句1中,所缺部分为宾语,而where, that, on which都不能起到宾语的作用,只有the one既做了主句的表语,又可做从句的宾语,可以省略关系代词,所以应选D.
而句2中, 主、谓、宾俱全,从句部分为句子的状语表地点,既可用副词where,又因 in the museum词组,可用介词in + which 引导地点状语.而此题中,介词on 用的不对,所以选A.
关系词的选择依据在从句中所做的成分,先行词在从句中做主、定、宾语时,选择关系代词 (who, whom, that, which, whose)； 先行词在从句中做状语时,应选择关系副词 ( where 地点状语,when 时间状语,why 原因状语) .
1) 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,例如：
This is the house which we bought last month. 这是我们上个月买的那幢房子.（限制性）
The house, which we bought last month, is very nice.这幢房子很漂亮,是我们上个月买的.（非限制性）
2) 当先行词是专有名词或物主代词和指示代词所修饰时,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) 非限制性定语从句还能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.
说明：关系代词that和关系副词why不能引导非限制性定语从句.
1）介词后面的关系词不能省略.
2）that前不能有介词.
3） 某些在从句中充当时间,地点或原因状语的"介词+关系词"结构可以同关系副词when 和where 互换.
This is the house in which I lived two years ago.
This is the house where I lived two years ago.
Do you remember the day on which you joined our club?
Do you remember the day when you joined our club?
由as, which 引导的非限定性定语从句,as和which可代整个主句,相当于and this或and that.As一般放在句首,which在句中.
As we know, smoking is harmful to one's health.
The sun heats the earth, which is very important to us.
典型例题
1）Alice received an invitation from her boss, ___came as a surprise.
A. it B. that C. which D. he
答案C. 此为非限定性从句,不能用 that修饰,而用which.,it 和he 都使后句成为句子,两个独立的句子不能单以逗号连接.况且选he句意不通.
2）The weather turned out to be very good, ___ was more than we could expect.
A. what B. which C. that D. it
答案B.which可代替句子,用于非限定性定语从句,而what不可.That 不能用于非限定性定语从句,it不为连词,使由逗号连接的两个句子并在一起在英语语法上行不通.
3）It rained hard yesterday, ____ prevented me from going to the park..
A. that B. which C. as D. it
答案B.
as 和which在引导非限制性定语从句时,这两个关系代词都指主句所表达的整个意思,且在定语从句中都可以作主语和宾语.但不同之处主要有两点：
(1） as 引导的定语从句可置于句首,而which不可.
(2） as 代表前面的整个主句并在从句中作主语时,从句中的谓语必须是系动词；若为行为动词,则从句中的关系代词只能用which..
在本题中,prevent由于是行为动词,所以正确选项应为B.
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).
例2. as可引导非限制性从句,常带有'正如'.
As we know, smoking is harmful to one's health.
As is know, 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.
1)Whoever spits in public will be punished here.
(Whoever 可以用 anyone who 代替)
2)The parents will use what they have to send their son to technical school.
(what 可以用all that代替)
1）what = the thing which；whatever = anything
What you want has been sent here.
Whatever you want makes no difference to me.
2) who= the person that whoever= anyone who
（错）Who breaks the law will be punished.
（错）Whoever robbed the bank is not clear.
（对）Whoever breaks the law will be punished.
（对）Who robbed the bank is not clear.
3) that 和 what
当that引导定语从句时 ,通常用作关系代词,而引导名词性从句时,是个不充当任何成分的连接词.宾语从句和表语从句中的that常可省略.What只能引导名词性从 句, 用作连接代词,作从句的具体成分,且不能省略.
I think (that) you will like the stamps.
What we need is more practice.
1）不用that的情况
a) 在引导非限定性定语从句时.
(错) The tree, that is four hundred years old, is very famous here.
b) 介词后不能用.
We depend on the land from which we get our food.
We depend on the land that/which we get our food from.
2) 只能用that作为定语从句的关系代词的情况
a) 在there be 句型中,只用that,不用which.
b) 在不定代词,如：anything, nothing, the one, all, much, few, any, little等作先行词时,只用that,不用which.
c) 先行词有the only, the very修饰时,只用that.
d) 先行词为序数词、数词、形容词最高级时,只用that..
e) 先行词既有人,又有物时.
举例：
All that is needed is a supply of oil.
所需的只是供油问题.
Finally, the thief handed everything that he had stolen to the police.
那贼最终把偷的全部东西交给了警察.

as

有.例如such…… as的组合
He is such a good student as everyone loves.