关系代词指的是代表引导词，同时在从句中作一定的句子成分。关系代词有主格、宾格和属格之分，并有指人与指物之分。关系代词用来引导定语从句。

关系代词有主格、宾格和属格（所有格）之分，并有指人与指物之分。that的用法最广，that 可指人也可指物。见表：

but，as，than作关系代词引导定语从句

hardly等）。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。

as既可指人，也可指物，常在限制性定语从句中充当主、宾、表语。as引导的定语从句的先行词前面常有as /such /the same等修饰词。例如： ①He is as brave a man as ever lived．他是世界上最勇敢的人。 ②Don’t read such books as are not worth reading．不要读那些不值得读的书。 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： ① Taiwan，as we all know，is an inseparable part of China． ②As we all know，Taiwan is an inseparable part of China． ③Taiwan is an inseparable part of China， as we all know．

than前通常有表比较的词。例如：Fewer friends than we had expected came to our evening party．来参加晚会的朋友比我们预料的还要少。

在使用上述三个特殊的关系代词时，还要注意区分下列两个词组：

定语从句

关系代词代表先行词，同时在从句中作一定的句子成分，如：

The girl whom I spoke to is my cousin.

跟我讲话的女孩是我表妹。（该句中whom既代表先行词the girl，在从句中作介词to的宾语。）

This is the pencil whose point is broken.

这就是那个折了尖的铅笔。（whose 指物，在限定性定语从句中作定语）

He came back for the book that he had forgotten.

他回来拿他忘记了的那本书。（that指物，在限定性定语从句中作宾语，可以省略）

which

如：

He said he saw me there, which was a lie.

他说在那儿看到了我，纯属谎言。

关系代词that在从句中作宾语或表语时可省略， 如：

I've forgotten much of the Latin I once knew.

我已经忘了很多曾经学过的拉丁语。

He's changed. He's not the man he was.

他变化很大，已不是过去的他了。

注释：关系代词在从句中作宾语时可省略，that在从句中作表语时也可省略。

非限定性定语从句中，不能用that作关系代词。

1.常用that 不用which的情况：

（1）先行词为不定代词all，little，few，much，anything，everything， nothing， something等时。

I will do all (that) I can to help you.

（2）先行词被序数词、形容词最高级或the only, the very等所修饰或其本身就是序数词﹑形容词最高级时。

He was the only person that joined the army in his village that year.

（3）先行词既有人，又有物时

They talked about the people and the things (that)they remembered in the school.

（4）当主句是以who 或which开头的疑问句时，定语从句用that 引导，避免重复。

Who is the boy that was here just now?

2.若关系代词在定语从句中作介词宾语，介词可提前至关系代词前，此时关系代词只能用whom或which。

关系词通常是用来引导定语从句的，但as，than和but这三个词却与which，who，that，where，when和why等典型的关系词不同｡三者本身具有常见的字面意义，前面有名词作先行词，但后面的定语从句却不像典型的定语从句｡这些既像连接词又像关系词的词，我们就姑且称它们为准关系词｡下面对其逐个作一分析：

that 的用法

（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.

（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，（恰恰，正好），any，few， little，no， all 修饰时，只用that。

（d）先行词由序数词、数词、形容词最高级修饰时，只用that。

（e）先行词既有人，又有物时

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。

不能用Which的几种情况

1.当先行词为all，little， much，few， everything， none 等不定代词时关系代词用that而不用which。

There are few books that you can read in this book store.

2.当先行词既有人又有物时，关系代词用that，不用which。

He asked about the factories and workers that he had visited.

3.当先行词有形容词最高级修饰时，关系代词用that， 而不用which。

Guilin is one of the most beautiful cities that I have ever visited.

4.当先行词有序数词修饰时，关系代词用that，不用which。

The first sight that was caught at the Great Wall has made a lasting impression on him.

5.当先行词被the only， the very， the same， the right等修饰时，关系代词用that，不用which。

It is the only book that he bought himself.

6.当先行词被all， every， any， much， little， few， no等修饰时，关系代词用that，不用which。

There is no clothes that fit you here.

7.当主句是以which开头的特殊问句时，定语从句关系代词一般用that而不用which。

Which of the books that had pictures was worth reading?

8.在强调句

It is in this room that he was born twenty years ago.

We need such materials as (not which) can bear high temperature.

Mary was late again, as had been expected.

11.As 引导的定语从句可以放在主句前面，也可以放在主句后面或主句中间，而由 which引导的定语从句只能放在主句后面。

As we all know, oceans cover more than 70% of the earth.

不可省略和可以省略

1.关系代词which，whom，who，that在定语从句中作宾语时可以省略。

Here is the man (who/that/whom)you've been looking for.

以下情况不能省略：

（1）在介词+whom与介词+which中，whom，which不能省略。

That is the headmaster with whom my father was talking just now.

（2）在非限制性定语从句中，作宾语的关系代词也不能省略。

The elephant is like a spear,as anybody can see.

（3）在the same...as，such...as，as...as，the same...that中，as，that即使作宾语，也不能省略I have bought the same bicycle as you have (bought). (指同类用as)

This is the same book that I read the day before yesterday. (that指同一个)

（4）当由and，but，or等连词连接两个或两个以上的定语从句修饰一个先行词时，第一个关系代词可省，但第二，第三个不可省略。

This is the book (which) I read yesterday and which I find very interesting.

2.当that在从句中作补语时可以省略。

She is all (that) a teacher should be.

3.在there be 结构中出现定语从句，或在定语从句中出现there be 时，用作主语的关系代词也可省略。

This is the best dictionary (that) there is in the library.

4.状语的省略

（1）当先行词是reason，而且定语从句中作原因状语时，关系代词可用why，that，也可以省略。

That is the reason (why) I did it.

（2）当先行词是way，且在定语从句中作方式状语时，关系代词可用in which，that，也可以省略。

I don't know the way （in which/that） leads to the top of the mountains.

(3)当先行词是time时，关系代词可用when，that 或省略。

I don't know the exact time (when/that) the sports meet will take place.

注意：关系代词作宾语有时也不能省略。