一、基本概念：
在複合句中，修飾某一名詞或代詞的從句叫定語從句。如：
Do you know the man who spoke at the meeting just now?
That is the house where he lived ten years ago.
定語從句所修飾的詞叫先行詞；定語從句一般用關係代詞或關係副詞來引導，關係詞放在先行詞與定語從句之間起連接作用，同時又作從句中的一個成分。
引導定語從句的關係代詞有：that, who, whom, whose, which;
關係副詞有：when, where, why.
二、關係詞的用法：
（一）關係代詞的用法：
1． 作主語用who, which和that, 如：
He is the man who/that lives next door.
The train which/that has just left is for Shenzhen.
2． 作賓語用whom, who, which, that, 如：
The man (whom/who/that) we have just seen is a famous writer.
Where is the book (which/that) I bought last week?
注：在非正式文體中，用於指人的關係代詞who whom, that 通常可以省略，但在正式文體中通常用whom, 不可省略；用於指物的關係代詞which和that 在非正式文體中也通常省略，但在正式文體中一般不省略。
3． 作定語用whose, 如：
(a) He is the man whose car was stolen last week.
(b) It was a meeting whose importance I did not realize at that time.
注：“whose +名詞中心詞”這一結構在定語從句中既能作主語（如上a句），又能作賓語（如上b句）。whose 的先行詞常用來指人，但有時也可以用來指具體事物或抽象概念，這時可以與of which 結構互換，詞序是：“名詞+of which”，如：
They came to a house whose back wall had broken down.. (= the back wall of which)
He’s written a book the name of which I’ve completely forgotten. (= whose name)
4． 作表語只用that ，它既可以指人，也可以指物，但時常省略。如：
He is no longer the man that he used to be.
This is no longer the dirty place (that) it used to be.
（二）關係副詞的用法：
1．when 指時間，在從句中作時間狀語，它的先行詞通常有：time, day, morning, night, week, year 等。如：
I still remember the time when I first became a college student.
Do you know the date when Lincoln was born?
注：when時常可以省略，特別是在某些句型和某些時間狀語中。如：
Each time he came, he did his best to help us.
But help never stopped coming from the day she fell ill.
2．where指地點，在從句中作地點狀語。它的先行詞通常有：place, spot, street, house, room,
city, town, country等，如：
This is the hotel where they are staying.
I forget the house where the Smiths lived.
注：where有時也可以省略。如：
This is the place (where) we met yesterday.
3． why指原因或理由，它的先行詞只有reason。如：
That is the reason why he is leaving so soon.
注：why時常也可以省略。如：
That is the real reason he did it.
(三) 使用關係副詞應注意下列幾點：
1． 這三個關係副詞在意義上都相當於一定的介詞+which結構：
when = on (in, at, during…) + which;
where = in (at, on…) + which;
why = for which. 如：
I was in Beijing on the day when (=on which) he arrived.
The office where (=in which) he works is on the third floor.
This is the chief reason why (=for which) we did it.
2． 當先行詞是表時間的time, day等和表地點的place, house等時，一定要注意分析從句的結構，如果缺少主語或賓語時，關係詞應該用which或that, 缺少時間狀語或地點狀語時，才能用when或where，試比較：
I’ll never forget the day when my hometown was liberated.
I’ll never forget the days which/that we spent together last summer.
His father works in a factory where radio parts are made.
His father works in a factory which/that makes radio parts.
3． when和where既可以引導限制性定語從句，也可以引導非限制性定語從句。而why 只
能引導限制性定語從句。
三．限制性定語從句與非限制性定語從句
1．限制性定語從句說明先行詞的情況，對先行詞起限定作用，與先行詞關係十分密切，不可用逗號隔開，也不可省略，否則全句意義就不完整。如：
This is the telegram which he refers to.
Is there anything (that) I can do for you?
2．非限制性定語從句只是對先行詞作補充說明，沒有限定作用，它與先行詞的關係比較鬆散，因而不是關鍵性的，如果省略，原句的意義仍然完整。這種從句在朗讀時要有停頓，在文字中通常用逗號與主句隔開。如：
This note was left by Tom, who was here a moment ago.
As a boy, he was always making things, most of which were electric.
引導非限制性定語從句的關係詞有：who, whom, whose, which, when 和 where，不可以用that和why。
另外，非限制性定語從句從意義上講，相當於一個並列句，在口語中使用並不普遍，在日常生活中，人們通常用並列句或簡單句來表達。如：
I told the story to John, who later did it to his brother.
= I told the story to John, and he later told it to his brother.
Yesterday I happened to see John, who was eager to have a talk with you.
= Yesterday I happened to see John and he was eager to have a talk with you.
3．兩種定語從句的內涵不同，限制性定語從句具有涉他性，而非限制性定語從句具有 唯一性，這在理解和翻譯時應特別注意。試比較：
All the books there, which have beautiful pictures in them, were written by him.
All the books there that have beautiful pictures in them were written by him.
His brother, who is eighteen years old, is a PLA man. （只有一個）
His brother who is a PLA man is eighteen years old. （不止一個）
4．有時，非限制性定語從句所修飾的不是某一個詞，而是整個主句或是主句中的一個部分，這時一般採用which或as來引導。如：
He passed the exam, which/as he hoped he would.
注：（1）as引導的從句可以放在主句之前，而which引導的.從句只能放在主句之後。
They are hollow, which makes them very light.
As is known to all, Taiwan is a part of China.
（2）從意義上講，which指前面主句的內容；而as指代的是作爲一般人都知道的常
識性的東西，因此常譯成“就象… …那樣”。
（3）如果定語從句的內容對主句的內容起消極作用，則用which，而不用as，如：
She stole her friend’s money, which was disgraceful.
He tore up my photo, which upset me.
5．在正式文體中，以the way爲先行詞的限制性定語從句通常以in which或 that 引導，如：
The way in which you answered the questions was admirable.
但在非正式文體中，人們通常省略in which或 that :
The way (in which) he spoke to us was suspicious.
I don’t like the way (that) you laugh at her.
四．關係詞的選擇
1． 在非限制性定語從句中，關係代詞作主語，只能用who 指人，which指物；關係代詞做賓語，常用whom（口語中有時用who）指人，which指物，它們都不能用that代替。
2． 關係代詞作介詞賓語，不論是在限制性定語從句中，還是在非限制性定語從句中，當介詞前置時，只能用whom指人，which指物；但如果介詞後置，則不受這種限制，關係代詞還可以省去，特別是在口語中。如：
Do you know the boy to whom she was talking?
Do you know the boy (that) she was talking to?
The pencil (which/that) he was writing with suddenly broke.
3． 在限制性定語從句中，當先行詞指物時，關係詞可用which或that，二者常可以互換；但在下列情況中，只能用that，不用which：
(1) 當先行詞是all, a lot, (a) little, few, much, none, anything, something, everything, nothing等詞時。如：
All that can be done has been done.
In this factory I saw little / much that was different from ours.
(2) 當先行詞被all, any no, much, little, few, every等限定詞所修飾時。如：
We heard clearly every word that he said.
(3) 當先行詞是序數詞或被序數詞所修飾時。如：
The first thing that should be done is to get the tickets.
When people talk about Hangzhou, the first that comes to mind is the West Lake.
(4) 當先行詞是形容詞最高級或被形容詞最高級所修飾，以及先行詞被序數詞和形容
詞最高級同時修飾時，如：
Is that the best that you can do?
That’s the most expensive hotel that we’ve ever stayed in.
This novel is the second best one that I have ever read.
(5) 當先行詞被 the very, the only, the next, the last等所修飾時。如：
This is the very book that I want to find.
(6) 當先行詞爲指人和指物的兩個並列名詞詞組時。如：
The guests spoke highly of the children and their performances that they saw at the Children’s Palace.
She described in her compositions the people and places that impressed her most.
(7) 當主句是以which開頭的特殊疑問句時。如：
Which is the car that killed the boy?
4. 在限制性定語從句中，當先行詞指人時，關係詞可用who(m)或that，二者常可互換。
但在下列情況中，用who(m)，而不用that：
(1) 當先行詞是one, ones, any, few, anyone, anybody, someone, somebody, everyone,
everybody等詞時。如：
Is there anyone who can answer this question?
He was among the few who managed to live through the enemy prison camp.
注：在非正式文體中可以說：You’re the one that knows where to go.)
(2) 當先行詞是he, they, those, people, person等詞時。如：
He who wants to catch fish just not mind getting wet.
Those who are against the proposal put up your hands.
注：在固定結構的諺語或習語中，可用he that…。如：
He that promises too much means nothing.
(3) 當先行詞有較長的後置定語修飾時。如：
Do you know the writer in blue with thick glasses who is speaking at the meeting?
(4) 在分隔式定語從句中，若先行詞指人，爲了明確修飾關係，應當用who(m)。如：
A new master will came tomorrow who will teach you German.
There’s only one student in the school who/whom I wanted to see.
I was the only person in my office who was invited.
(5) 兩個定語從句同時修飾一個指人的先行詞，第二個定語從句常用who(m)來引導，如：
She is the only girl I know who can play the guitar.
5. 在限制性定語從句中，當先行詞指人時，在下列情況中，一般用關係詞that:
(1) 當主句是以who或which開頭的特殊疑問句時。如：
Who is the man that is reading the newspaper over there?
Which of us that knows anything does not know this?
(2) 當先行詞被形容詞最高級或序數詞所修飾時。如：
He is the greatest man that has ever lived.
(3) 當先行詞被the only, the very, the last等詞所修飾時。如：
She is the only person that understands me.
6. 當先行詞被the same所修飾時，關係詞既可以用as，也可以用that。在表示具體事物
時，有時兩者有一定的區別。一般說來，表示同一種類多用as，表示同一事物多用that。
如：
This is the same instrument that I used yesterday. 這就是我昨天用過的那臺儀器。
This is the same instrument as I used yesterday. 這臺儀器跟我昨天用過的那臺一樣。
在抽象概念上，同種類和同一事物是沒有絕對區別的，所以兩個詞可換用：
I have the same opinion as / that you have.
這裏要注意的是：
（1） 使用as時，它引導的定語從句中的動詞可以省略，但使用that時，定語從句中
的動詞不可省略。如：
Women received the same pay as men.
Women received the same pay that men received.
(2) 在“the same…that”結構中，that只是用來加強語氣，強調“相同”。that可以省去而不改變句子原意，甚至連名詞前的same也可以省去。如：
This is the same instrument that I used yesterday.
= This is the same instrument I used yesterday.
= This is the instrument I used yesterday.
但在“the same…as”結構中，same和as都不能省略。
(3) 當“the same…that”結構中的that作爲關係副詞用時，不可以直接與as互換。
如：
He lives in the same building that I live.
= He lives in the same building as / that I live in.
Shall we meet at the same place that we last met?
= Shall we meet at the same place that / as we last met at?
7. 當先行詞前有such, so, as時，關係詞應當用as。如：
A wise man seldom talks about such things as he doesn’t understand.
He spoke in such easy English as everybody could understand.
At this time of the day, all buses and trolleys have to carry as many passengers as they can.
It is so easy a book as every schoolboy can read.
Let’s discuss such things as we can talk of freely.
另需注意：
This book is written in such easy English as beginners can understand.（定語從句）
This book is written in such easy English that beginners can understand.（結果狀語從句
