定语从句是形容词性从句， 用来修饰主句中的名词或代词。其作用相当于定语，故称定语从句。 被定语从句所修饰的对象称为先行词。 定语从句一般紧随它所修饰的先行词之后, 并由关系代词或关系副词引导。
(1) 由 that 引导的定语从句
that 可以指人或物。 在定语从句中作主语、宾语或表语， 作宾语或表语时可以省略。
The man that visited our school is from Australia．到访我们学校的那个人来自澳大利亚。
Is oxygen the only gas that helps fire burn? 氧气是唯一的助燃气体吗？
The girl (that) I saw is called Mary. 我见到的那个女孩名叫玛丽。
Is there anything else (that) you require? 你还需要别的东西吗？
My hometown is no longer the place (that) it used to be. 我的家乡再也不是以前那个样子了。
（2）由 which 引导的定语从句
which 指物， 在定语从句中作主语或宾语。
I do not like stories which have unhappy endings.我不喜欢有不幸结局的小说。
That was a fault which could not be forgiven. 那是不能饶恕的错误。
Have you seen the watch (which) I left here just now? 你看到我刚才放在这里的手表了吗？
These are the wires with which different machines are connected. 这些是连接不同机器的电线。
The reason for which he refused to go to the party was that they had not invited him to.
（3）由 who 引导的定语从句
Anybody who breaks the laws will be punished. 任何违反法律的人都将受到惩罚。
Do you know the boys who are standing over there? 你认识站在那边的那些男孩吗？
[注] 在口语中，可以用who代替whom, 在定语从句中作宾语。
The man who I saw told me to wait. 我见到的那个人叫我等。
I know the man who you were speaking to just now. 我认识你刚刚和他讲话的那个人。
The doctor whom you are waiting for has left. 你一直在等的那位医生已经离开了。
Is she the very person whom we must take good care of? 她就是那个我们必须好好照顾的人吗？
They are looking for the patient on whom doctors just performed an operation.
There are some students whose questions I can’t answer. 有些学生的问题我回答不了。
They lived in a room whose window opened to the south. 他们住在一间窗户朝南开的房间里。
Once there was a wise king whose name was Alfred.
Can you see the mountain whose top is covered with snow?
(1) 由when 引导的定语从句
I’ll never forget the days when I worked with you. 我永远不会忘记我与你共事的日子。
Can you still remember that evening when we met for the first time?
(2) 由 where 引导的定语从句
This is the town where I was born. 这是我出生的城市。
She would like to live in a country where it never snows. 她喜欢住在不下雪的国家。
Who can think of a situation where this phrase can be used? 谁能想出用这个短语的情况？
Her career has reached the stage where she must decide what to do next.
I’ve come to the point where I can’t stand him. 我已经到了无法忍受他的地步。
(3) 由 why 引导的定语从句
I don’t know the reason why he didn’t tell it to his father.
That’s the reason why she left home. 那就是她离家出走的原因。
Is this the reason why he refused our offer? 这就是他拒绝我们帮助他的理由吗？
We can’t accept the excuse why you were absent. 我们无法接受你缺席的借口。
This is the explanation why they put off the meeting. 这是他们为何推迟会议的解释。
You may go there any time you like. 你随便什么时候都可以去那儿。
By the time you arrive in London, we will have stayed there for two weeks.
I still remember the first time I met her. 我仍然记得我第一次见他的时候。
Each time he goes to business trip, he brings a lot of living necessities.
Do you know the year the book was published? 你知道那本书出版的年份吗？
(2) where 有时也可以省列
This is the place they met yesterday. 这就是他们昨天碰头的地方。
That is the place I was born. 这是我出生的地方。
(3) 先行词为way 时，定语从句的引导词也可以省列。
I don’t like the way he laughed at me. 我不喜欢他用那种方式来嘲笑我。
Do it the way I showed you. 按我教你的那样做。
Stop kicking my dog, or I will treat you the way you treat it!
(1) 当先行词是anything, everything, nothing, something, few, all, none, little, some 等不定代词时。
Finally, the thief handed everything that he had stolen to the police.
This is all that I want to say at the meeting. 这就是我在会上要说的。
I have nothing that is worth reading. 我没有什么值得一读的东西。
Is there anything that I can do for you? 有什么我可以帮你的吗？
Every car that has a high price is worth what it costs. 每辆高价的车都有它的价值。
You are the first person that I want to ask for. 你是我要见的第一个人。
This is the second book that I have ever written. 这是我写的第二本书。
This is the most beautiful city that I’ve ever seen. 这是我见过的最漂亮的城市。
The dinner was the most expensive meal (that) we had ever had. 那是我们吃过的最贵的晚餐。
(4）当先行词被the very, the only, the same, the last 修饰时。
This is the only painting in this style that we have. 这种风格的画我们仅有一幅。
This is the very pen that I am looking for. 这正是我找的钢笔。
You are the last person that I want to see. 你是我最不想见到的人。
This is the same pen that I lost last week.这就是我上周丢失的那支钢笔。
(5) 当先行词前面有who, which 等疑问代词时。
Who that you have ever seen can beat him in chess? 你曾见过谁能在棋艺上打败他？
Which is the book that you bought yesterday? 那本是你昨天买的书？
He talked happily of the writer and his books that interested him.
The professor and his achievement that I heard about are admired by them .
非限制性定语从句与先行词的关系松散，只起补充说明的作用。 去除非限制性定语从句对主句的意义影响不大。非限制性定语从句由逗号隔开，在翻译成中文时，常可译成一个并列句。引导非限制性定语从句的关系代词有 which, who, whom, whose, as; 关系副词有 when 和 where。 非限制性定语从句不能由关系代词that引导。
1) 由which 引导的非限制性定语从句
Her house, which was built a hundred years ago, stood still in the earthquake.
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。
Recently I bought an ancient Chinese vase, the price of which was very reasonable.
注: which 有时不代表一个名词， 而是代表前面整个句子或句子的一部分。
The sun heats the earth, which makes it possible for plants to grow.
He didn’t pass the exam，which disappointed me. 他没通过这次考试，令我很失望
2) 由 who 引导的非限制性定语从句
Charlie Chaplin, who died in 1977, is considered one of the greatest and funniest actors in the history of the cinema.
Charles Smith, who was my former teacher, retired last year.
3) 由 whom 引导的非限制性定语从句
He was eager to go to the hospital to see his stepmother, whom he loved and respected as his own mother.
Her sons, both of whom work abroad, rang her up this morning.
The eighty-nine passengers all escaped without serious injury，four of whom were Americans.
4) 由 whose 引导的非限制性定语从句
Look at the building, whose roof is white. 看那栋楼，楼顶的颜色是白的。
5) 由 when引导的非限制性定语从句
He will put off the picnic until May 1st, when he will be free.
At the time when I saw him, he was well. 我见到他那时，他身体还不错。
6) 由 where引导的非限制性定语从句
They went to London，where they lived for six months.
Some pre-school children go to a day care center, where they learn simple games and songs.
They stood on the top of the building, from where they could see the whole city.
1）由 whereby, wherein, whereupon 引导的定语从句
They have set a plan, whereby you can spread your costs.
He gazed once more around the room, wherein was assembled his entire family.
I told her that she looked fat, whereupon she threw the saucepan at me and burst into tears.
2）as 和such 相互搭配引导的定语从句。
He’s not such a fool as he looks. 他没有他看起来那么傻。
I never heard such stories as he tells.我从未听过他讲的这类故事。