代词之中，最为令人头痛的，或许莫过于关系代词了。咋一听，是不是有点迷糊：啥叫关系代词？先看个例子：The girl who is reading is my sister.在这个句中，who就是关系代词，代指先行词the girl。哦，宝宝们恍然大悟：原来代指定语从句中先行词的代词，就叫关系代词！！！
英语中，关系代词主要有that, which, who, whom, whose, of which, as等。
关系代词不仅代指先行词，还在定语从句中担当主语、宾语、表语和定语。如：
Lily likes music that is quiet and gentle.玛丽喜欢轻柔的音乐。（that作主语）
The film (which)we saw yesterday was wonderful.我们昨天看的那部电影很好看。（which作宾语）
He is no longer the man (that) he was ten years ago.他不再是十年前的那个他了。（that作表语）
The dress whose color is red is bought by my mom.红色那件裙子是我妈妈买的。（whose作定语）
这些关系代词有主格，宾格和属格之分，以及指人与指物之分。如表所示：
1.that可用于指人或物。在从句中作主语或宾语，作主语时不可省略，作宾语可省略。例如：
I like books that are interesting.我喜欢有趣的书。（that作主语）
The book (that) I put on the table is Tom’s.我放在桌子上的那本书是汤姆的。（that作宾语）
2.which用于指物，在句中作主语或宾语，作主语不可省略，作宾语可省略。另外，which还可以引导非限制性定语从句。例如：
The book which is on the desk seems very interesting.桌上那本书貌似很有趣。（which作主语）
The book (which) we saw last night was wonderful.我们昨天晚上看的那本书很不错。（作宾语）
He said the book was so easy, which was not true.他说这本书很简单，那是不对的。（which引导非限制性定语从句）
3.who/whom用于指人，who用作主语，whom用作宾语。在口语中，有时可用who代替whom，也可省略。例如：
The girl who wears red is from England.穿红色衣服的那个女孩是英国人。（who作主语）
The man (whom) Lucy is talking to is my teacher.正在与露西谈话的那个人是我的老师.（whom作宾语）
4.whose用作关系代词时，表示“……的……”：
The students whose names were called stood up.被叫到名字的学生站了起来。
The house whose windows are broken is very old.窗户坏掉的那个房子很旧。
5.特殊关系代词but，as，than
（1）but既可指人或物，常在定语从句中充当主语。but本身含"否定"的意思，其作用相当于"that /which /who...not"。它前面的主句通常有"否定"的词。but引导的肯定定语从句和否定的主句连用，达到强烈肯定的修饰效果。例如：
There is no mother but loves her own children．（=There is no mother that/who does not love her own children．）没有不爱自己孩子的母亲。
（2）as可指人或物，常在限制性定语从句中充当主、宾、表语。
as引导的限制性定语从句的先行词前面常有as /such /the same等修饰词。例如：
He is as brave a man as ever berthed.他是世界上最勇敢的人。
as作关系代词，还可用来引导非限制性定语从句，as引导的定语从句可放在句首、句中或句末。例如：
As we all know, English is very important now．
English, as we all know, is very important now．
English is very important now, as we all know．
（3）than可指人或物。than前通常有表示比较的词。例如：
Fewer guests than we had expected came to the party．来参加晚会的客人比我们预料的还要少。
关系代词引导限定性定语从句和非限定性定语从句，有的时候关系代词可以省略，何时省略的具体说明如下：
We went to a beach (which/what) Ali had recommended to us.该句中的关系代词是which/what，可省略，修饰的是beach，引导的从句主语是Ali。
I know a man who/that ran in the New York Marathon last year.该句中的关系代词是who/that，修饰的是a man，引动的从句主语依然是a man。当关系代词修饰的对象和从句中的主语是相同的，则该关系代词不能省略。
关系代词在限定性定语从句中：
形容物的时候，口语中用that书写中用which作宾语（或省略关系代词），例如：
Decorating's job (that) I hate. （口语中比...which...更合适）
形容人时，口语中通常用that作宾语（或省略关系代词）而不是who或whom，例如：
He's the man (that) I met at Aisha's party. （比...who/whom I met...更合适）
whom通常出现在非常正式的书写中，口语中极少用到，例如：
The boy whom Elena had shouted at smiled. （用that，who或省略关系代词会不那么正式一点）
作为主语并且跟在something和anything后面，作为代词跟在all, little, much,none以及包含最高级的名词短语后面时关系代词用that。which也可以作为主语跟在something, anything 后面，但是没有that常见，例如：
These walls are all that remain of the city. （不是...which remain of the city）
that可以作为宾语（或省略关系代词）跟在something/anything,all等单词以及含最高级的名词短语后面，例如：
She's one of the kindest people (that) I know. （不是...one of the kindest people who I know.）
关系代词在非限定性定语从句中：
在非限定性定语从句中关系代词不能省略
who或whom可以作宾语，whom用在正式书写中，例如：
Professor Johnson, who(m) I have long admired, is to visit the university next week.
形容物的时候，which可以作主语或宾语，that有时可以代替which，但有些人会觉得用that不正确，例如：
The Master's course, which I took in 2001, is no longer taught. （或者...that I took...）
whose引导的从句
书写中谈到某物属于某人或与某人、动物、植物有关时，用关系代词whose+名词引导关系从句，例如：
Stevenson is an architect whose designs have won international praise.
Suzy was taking care of a dog whose ears were badly damaged in a fight with a cat.
whose可以引导限定性或非限定性从句。
通常谈到某物属于或关联另一物时不用whose，例如：
I received a letter, and its poor spelling made me think it was written by a child. （比I received a letter, whose poor spelling made me think...更自然）
然而有的时候谈到城镇、国家或机构用whose，例如：
The film was made in Botswana, whose wildlife parks are larger than those in Kenya.
We need to learn from companies whose trading is healthier than our own.
学术报告中whose可以表示广泛的所属关系，例如：
Students have to solve problems whose solutions require a knowledge of calculus.
when, whereby, where和why引导的关系从句
这些关系代词可以引导关系从句或其它类型从句。when表时间，whereby表方式方法（通常出现在正式书写中），where表地点。书写中，由介词+which的短语通常可以替代上述提到的这些关系代词，例如：
The camera records the time when the photo is taken. （或...the time at which...）
Do you know the date when we have to hand in the essay? （或...the date on/by which...）
We need to develop a system whereby workers and management can communicate more effectively. （或者...the systme in/by which workers...）
This was the place where we first met. （或者...the place at/in which we...）
学术英语中，可以用where表示除地点以外的内容，尤其是跟在case, condition, example, situation, system这些单词后面，例如：
Later in this chapter we will introduce cases where consumer complaints have resulted in changes in the law. （或更正式的表达为...cases in which...）
固定搭配的形式有a/the reason why或a/the reason that或只有a/the reason，例如
I didn't get a pay rise, but this wasn't the reason why I left. （或者...the reason (that) I left.)
who, what, whatever, whoever和whichever引导的从句
某些由wh-单词引导的从句在句中起到名词短语的作用，称为名词性关系从句，例如：
Can you give me a list of who's been invited?(=a list of the people who have been invited)
I didn't know what I should do next. (=the thing that I should do next)
what不适用于下面句型中：
I managed to get all the books that you asked for. （不能是...all the books what you asked for.）
不确定或不知道谈论的物或人时，可以用whatever, whoever, whichever，例如：
I'm sure I'll enjoy eating whatever you cook.
Whoever wins will go on to play Barcelona in the final.
Whichever one of you broke the window will have to pay for it.
还是不太理解，关系代词和代词的区别啊，😂
英语中的关系代词常用来引导定语从句。关系代词作为连接两个句子的部分：一方面它们在定语从句中担任一个成分，如主语、宾语、表语或定语；另一方面又代表定语从句所修饰的名词或代词（通常称为先行词）。常见的关系代词有: