概述
在功能上，关系子句当做形容词使用。
关系子句并没有外加连接词，而是将一个内含的重复元素改写为关系词。
构造前提:子句和主句之间必须要有关系，必须有一个重复的元素，将这个重复的元素改写为关系词，构造出关系子句。
在关系子句中可能是代名词改写为关系代名词、也可能是副词改写为关系副词，主要子句中的先行词一定是名词类，而从属子句中，不论是关系代名词还是关系副词，他所引导的关系子句一定是形容词子句，修饰先行词。
I know something which nobody else knows.
关系代名词
先行词如果是【人】，那么关系代名词就是who，如果先行词是【事、物】，那么关系代名词就是which，另外，不论先行词是人还是物，关系子句只要具有指示【限定】功能，指出哪一个，哪一些，那么关系代名词都可以采用that来取代。
Who的用法(包括whom、whose、that)
主词位置
People who live in glass houses shouldn’t throw stones.
who不可省略，因为具有指示功能，可以被that替代
受词位置
代表【人】的关系代名词，主格是who、受格是whom，但是一般忽略主格受格的差别，除非关系代名词放在介系词后面，必须采用受格whom。
Jack is a man who I trust completely.
Jack is a man whom I trust completely.
Jack is a man that I trust completely.
Jack is a man I trust completely.
介系词的受词位置
Jack is a man who you should talk to.
Jack is a man whom you should talk to.
Jack is a man to whom you should talk.
补语位置
After the stroke,John is not the man who(that) he used to be.
After the stroke,John is not the man he used to be.
所有格
如果先行词是人，从属子句中与其有交集的就是人称代名词的所有格(如his,her,their等)
Jack is a man whose judgement I trust.
Which的用法(包括that)
如果先行词是[物]，关系代名词应采用which，它引导的关系子句如果具有指示概念股能(关系子句前没有逗号隔开)，那么这个关系代名词也可以改写为that。
主词位置
I like the movies which(that) make me think.
受词位置
The movie which(that) I saw last night was excellent.
介系词的受词位置
My favorite movies are those in which all ends well.
That chair on which you are sitting is an antique.
That chair which(that) you are sitting on is an antique.
补语位置
The name which John calls his dog is a really odd one.
所有格
which本身缺乏所有格，有两种方法；一是借用who的所有格whose，二是采用of which来表示
I saw a mountain whose top was completely covered in snow.
I saw a mountain the top of which was completely covered in snow.
I saw a mountain of which the top was completely covered in snow.
主要子句为先行词
关系子句前以逗号和主要子句相隔，那么先行词很可能是前面整个主要子句
The whole house was overrun with ants,which was rather weird.
注意：which的后面是was，说明which代表的是前面的整句话，如果是were，那么久代表ants
下面是一个模棱两可的例子：
The whole house was overrun with ants,which frightened the vistor.
这里的which可能代表house，也可能代表ants
修改一：
The whole house was overrun with ants,a sight which frightened the vistor.
此时，which表示“这番景象”
The whole house was overrun with ants,nasty insects which frightened the vistor.
此时,which代表蚂蚁
指示功能
非限定性用法—关系子句放在括弧里面，表示这个关系子句不重要，只是可有可无的补充说明。此时，关系代名词只能用who或which，不能改为that，而且不能省略。
I met a friend who(that) went to the same high school with me.
这样理解，friend是一个模糊的概念，此时不知道是哪一个friend,所以后面的关系子句指出”到底是哪一个friend”
I met Jack Wang,who went to the same high school with me.
在这里,Jack Wang是一个名字，是确定的，后面的名词子句只是对它的补充
何时该用that
当关系子句有强烈的指示功能时，采用that比较好
如：
一、先行词是all,anything,everything之类标出了【明确范围】
二、先行词有first,next,last,only等限定词在内，或者最高级修饰语，产生了明确的指示
You are the only person that really understands me.
何时不能省略
非限定关系从句
My uncle Tom,whom you met the other night,is quite a character.
关系从句的位置
总的原则是不要造成句意模糊不清，句型清晰，各个修饰成分的修饰对象也要明确
I found a book which focuses on social relations in the liarbry. 不佳
int the library修饰模糊
In the library I found a book which focuses on social relations.
关系副词
常用的关系副词有when,where,how,why这四个。主要子句中的先行词仍然是名词，所以关系副词引导的关系子句仍是形容词。
一、when
The earthquake hit at a time when(that) most people were sound asleep.
该关系子句具有指示功能,可用that代替，也可省略
二、where
The artist lived in a place(that) where it was impossible to work.
三、how
I never found out the way how(that) he escaped.
四、why
The man didn’t explain the reason why(that) he wanted a divorce.
有逗号隔开时
注意:只有when和where引导的关系子句可以用逗号和先行词隔开，不具有指示功能
Written history of American begin in 1492,when Christopher Columbus arrived with his ships.
The civilization of ancient Egypt was born along the Nile,where the soil was kept fertile by annual floodings.
混淆点
一、Wh-的混淆
关系词，包括关系代名词(who,which)与关系副词(when,where,how,why)
关系代名词
Paris,which has a long history,is a legendary city.
关系副词(when、where前可用逗号分隔,why、how不可)
I will never forget my high school days,when life seemed so simple.
Let’s spend the weekend at Tommy’s,where we can be quite free.
Please show me the way how I can start this motorcycle.
Money is one reason why I don’t take any vacations.
疑问词(who,which,what,when,where,how,why)。疑问词引导的子句是由疑问句改写而来的名词子句
外加从属连接词(when,where)。引导的是副词子句，修饰动词的时间和地点
Wh-ever的混淆
复合的关系代名词(what,whatever,whoever,whichever),解释为anything that,anyone that等，引导的子句是名词子句
Whoever,whichever,whatever,whenever,whereever,however，用法相当于在疑问词who,which,what,where,how前面加上no matter，表示让步语气，引导的是副词子句。
That的混淆
直述句外加无意义的连接词that，引导的是名词子句
外加(so that,such that,in order that,in that)等有意义的连接词，引导的是副词子句
that是关系词，改写子关系代名词(who,which)与关系副词(when,where,how,why)，引导的是具有指示功能的关系子句
