導語 ：所謂從句，就是一個主謂結構相當於整個句子(這樣的句子叫複合句)的一個成分，因此從句不能單獨使用。在複合句中修飾名詞或代詞、作定語的句子叫定語從句。定語從句是中國人學英語最重要的難點之一。
其實定語從句很有規律，總結如下:在關係代詞中that既可指人又可指物、既可作主語又可作賓語，因此，除了在非限定性定語從句中，用that一般不會出問題。
關係副詞的用法比較單一，它們從句中只起狀語的作用，表示時間的就用who門，表示地點的就用where，而why只修飾一個詞，即reason。
定語從句所修飾的詞叫“先行詞”，因為它總是處在定語從句的前頭，比定語從句先行一步。
引導定語從句的詞叫關係詞，包括關係代詞和關係副詞。
關係代詞：
who，which，that作從句的主語
whom，which，that作從句的賓語(可省略)
whose從句中作定語
以下情況只能用that，不能用which:
i. 先行詞為不定代詞all, little, none，any，every，no，much, anything, nothing
ii. 先行詞有最高階和序數詞修飾時(包括: the only, the very, the same, the last, the next等)
iii. 先行詞既有人又有物的時候
以下情況只能用which，不能用that;
① 引導非限制性定語從句(包括代表整個主句的意思時)
② 介詞+關係代詞的結構中
關係副詞：
when指時間，在定語從句中作時間狀語
where指地點，在定語從句中作地點狀語
why指原因，在定語從句中作原因狀語，只修飾reason。
如果用定語從句把兩個句子合二為一：首先找出兩個句子當中相同的部分，定語從句修飾的就是這一部分。要把其中一個句子變成定語從句，就要把這句中相同的那個部分用一個關係詞來代替;代替時，先看被代替的部分是指人還是指物、再看它作什麼句成分。指人並作主語的，就用who。或that;指人並作賓語的，就用whom或that;指人並作定語的，就用whose。指物並作主語的，就用which或that認指物並作賓語的，還是用which或that認是物並作定語的，就用whose或of which。這樣找好並替換以後，再把這個關係代詞放到要變成定語從句的那個句子的最前面(被代替的部分不能再保留，其它的詞語一律不變)，這個句子就變成了定語從句。然後，再把這個定語從句整個放在被修飾的詞後面，最後，如果還有其它句子成分，就把它們放到定語從句的後面，就行了。例如：
Have you found the book? You were looking for the book yesterday.
在這兩個句子中，the book是相同的，定語從句修飾的就是the book。把後面這一句變成定語從句，找個關係詞來代替the book;在將要被變成定語從句的名子中，the book是物並作賓語，所以用which或that代替它。
然後把which或that放到本句的最前面，其它的詞和語序一律不變。這時，就成了"that/which you were looking for yesterday?”，再把這個定語從句整個放在被修飾的詞後面，就成了“have you found the book that/which you were looking for yesterday?”定語從句就完成了，主句是問句，所以句末用問號。that/which代替的是原句中的賓語，原句變成了從句，它們仍然作從句的賓語。關係代詞在從句中作賓語時可以省略，因此上句又可變成“have you found the book you were looking for yesterday?”.
關係副詞與此同理。只是關係副詞代替的是原句中的狀語。在被代替之前，這個狀語中一定要含有一個與另一句相同的成分。
例如：This is the house where I was barn and brought up in the house.在這兩個句子中，in the house是句子裡的地點狀語，定語從句修飾的就是the house。把後面這一句變成定語從句。在將要被變成定語從句的句子中，in the house是地點狀語，所以用where來代替它。然後再把where放到本句的最前面，其它的詞和語序來代替它。然後再把where放到本句的最前面，其它的詞和語序一律不變。這時，就成了"where}was barn and brought up"。再把這個定語從句整個放在被修飾的詞後面，就成了"This is the house where I was barn and brought up.”，定語從句就完成了，主句是陳述句，所以句末用句號。Where代替的是原句中的狀語，原句變成了從句，它就作從句的狀語。
那麼，“介詞+關係代詞”是怎麼回事呢？原來上面這個例句，還有一種做法：This is the house. I was born and brought up in the house.在這兩個句子中，the house是相同的，定語從句修飾的就是the house 。把後面這一句變成定語從句。在將要被變成定語從句的句子中，the house表示物而且是介詞in的賓語，所以用關係代詞which或that來代替。然後把which或that放到本句的最前面，其它的詞和語序一律不變。這時，後面這一句就成了 “which/that I was born and brought up in”。再把這個定語從句整個放在被修飾的詞後面，就成了“This is the house which/that I was born and brought up in”。定語從句就完成了，主句是陳述句，所以句末用句號。
which/that代替的是原句中的賓語，原句變成了從句，它們就作從句的賓語。關係代詞在從句中作賓語時可以省略，因此上句又可變成“This is the house I was born and brought up in.”
但是，in可以提到關係代詞的前面，不過這時不能用that，而且不能省略。所以上句又可變為“This is the house in which I was born and brought up.”這就是“介詞+關係代詞”的來歷。
定語從句又分為限定性定語從句和非限定性定語從句。限定性定語從句把它的先行詞限定在特定的意義之內，對先行詞起限定的作用、是先行詞必不可少的修飾語，沒有它，整個句子的意思就會受到影響、就不完整。非限定性定語從句不對先行詞起限定的作用，不是先行詞必不可少的修飾語，只對先行詞起補充說明的作用，沒有它，整個句子的意思不會受到影響、仍然完整。非限定性定語從句相當於一個分句，翻譯時也是把它當作分句處理的。非限定性定語從句和它的先行詞之間要用逗號隔開;而限定性定語從句和它的先行詞之間不能用逗號隔開。非限定性定語從句中除了不用that以外，其它關係詞都可使用，使用方法與限定性定語從句一樣。
例如：The supermarket which was opened two months ago is now closed down.兩個月前開的那家超市現在已經倒閉了。(限定)
The supermarket, which was opened two months ago, is now closed down.那家超市現在已經倒閉了，那家超市兩個月前開的。(非限定)
The book(which) you’re reading is mine .你正在讀的那本書是我的。(限定)
The book, which you’re reading, is mine.那本書是我的，你正在讀那本書。(非限定)
如果以上例子的差別不十分明顯，再看下面的例句：
I’ve been to London , which is a beautiful city.我去過倫敦，那是個美麗的城市。
Your father, whom I respect very much, is a kind old man.你父親是個很和善的老頭，我很尊重他。
Nanjing, where I lived for five years, is very hot in summer.南京夏天非常熱，我在那裡生活過五年。
在以上三例當中，定語從句不就能是限定性的。若變成限定性定語從句，其意就成了“我去過那個是座美麗的城市的倫敦。你那個我很尊重的父親是個很和善的老頭。我在那裡生活過五年的南京夏天非常熱。”言外之意是還有別的倫敦、父親和南京。
通過這幾個例子我們可以看出，專用名詞以及世界上獨一無二的東西都不能有限定性定語從句。因為它們的意義本身已經非常清楚，不需要對其進行限定。另外，非限定性定語從句的先行詞還可以是整個主句所表達的意義。
如：He did well in the physics exam, which surprised me.他物理考得很好，這使我很吃驚。
(學地道的英語有兩個重要的練習方法：parallel writing, and reverse translation，即平行寫作和逆翻譯。所謂平行寫作，就是模仿英語的句子寫類似的句子。而逆翻譯就是先把英語譯成漢語，或根據漢語的譯文，再把漢語翻譯成英語，再把英語譯文同原文比較，分析差異。這兩種方法能避免漢語式英語。)
He did well in the physics exam, which surprised me.他物理考得很好，這使我很吃驚。
請把這句話逆翻譯。有的同學會翻譯為：He did well in the physics exam, this surprised me. 這句話錯在什麼地方呢?錯在句法。這句話有兩個主謂結構，是兩個並列的分句，但沒有連詞(this 是代詞)，這就成了串句。
再如：He’s very particular about wording, which I am not.他很咬文嚼字，而我不。
I said nothing, which made her angry.我什麼也沒說，這使她很生氣。
Tom didn’t go to the show, which was a pity.沒去看演出，這很遺憾。
注意各個關係詞的用法：
1.指人的關係代詞：who, whom, whose, that 的用法：
(1)作主語(who, that )
Those who are going to play in the match are to meet at the gate at 1:30 after lunch.那些參加比賽的人午飯後1：30在大門口集合。
在本句中，先行詞是those;關係代詞who引導定語從句，同時代替先行詞在從句中擔任動詞are going to play 的主語。
The man who/that is talking with Mr. Wang is a famous doctor.正在和王先生說話的那個人是一個有名的醫生。
在本句中，先行詞是the man;關係代詞who/that引導定語從句，同時代替先行詞在從句中擔任動詞is talking的主語。
這個複合句可以還原成兩個句子：The man is a famous doctor. He is talking with Mr. Wang.
(2)作賓語包括作介詞賓語(whom, that )。此種情況下的關係代詞可以省略;
This is just the man(whom/that) I want for the job. 這正是我要的做這份工作的人。
在本句中，先行詞是the man;關係代詞whom/that 引導定語從句，同時代替先行詞在從句中擔任動詞want 的賓語。
Is he the manager (whom/that) you are looking for?他是你在找的那位經理嗎?
(3)當關系代詞緊跟介詞作介詞賓語時，不能用that，也不能省略，
如：The book from which I got a lot of useful information was written by a famous scientist.我從中得到許多有用資訊的那本書是一位著名科學家寫的。
Who is the boy with whom you were talking a moment ago.你剛才和他說話的那個男孩是誰?
I know the young couple from whose house the music is coming.但是當介詞放在從句末尾時，作為介詞賓語的關係代詞可以用that 並且可以省略。
如上頭兩句可改為：
The book (that /which) I got a lot of information from was written by a famous scientist.
Who is the boy (that/whom) you were talking with a moment ago?
2.指物的關係代詞which和that的用法：
(1)作主語
This is the instruction manual which/that tells you how to operate the computer.這是那本教你如何操作計算機的說明手冊。
(2)作賓語包括作介詞賓館。此種情況下的關係代詞可以省略：
The chair (which /that) you broke yesterday is now being repaired.你昨天弄壞的那把椅子現在正在修理。
The film (which/that) I saw last night was about a soldier who fought in WWII.
我昨天晚上看的那部電影是關於一個在二戰中打過仗的士兵的。(本句有兩個定語從句。)
This is the bike for which I paid $ 100.這就是我花了100美元買的那輛自行車。
The car(which/that)he went in was a black Cadillac.他坐在裡面走了的那輛汽車是一輛黑色的卡迪拉克。
The accounts of the company, (which/that) I’ve been payinggreat attention to, are in balance.我一直非常注意的公司賬目，是保持平衡的。
e 和of which 指代人或事物，作定語。of which 可用whose 代替;
The car whose lights (of which the lights/the lights of which) were all broken was my father’s.那輛所有的燈都破了的汽車是我父親的。
例：His house of which the windows (the windows of which /whose windows) were all broken was a depressing sight.他那所有窗戶都壞了的房子真是目不忍睹。
That is the book whose cover (of which the cover/the cover of which ) was broken.這就是那本封皮破了的書。
4.關係代詞的格應與它在從句中充當的成分一致。特別要注意插入語，
如：Peter is the one who everybody believes will fail to bring off the contract. Peter是那個人人都認為不能完成合同的人。(everybody believes 是插入語)
At the election I voted for the man whom I believed to be the most suitable.在選舉的時候我投了我認為最合適的那個人的票。
5.關係代詞作從句的主語時，從句的動詞必須和先行詞的人稱和數一致：
例：These are the operating instructions that/which are written in English.這就是用英文寫成的使用說明。
Are you staying at the white house which/that is newly completed and which /that has 15 bedrooms, 3 kitchens and 4 toilets?你是住在那幢剛剛竣工、有15個臥室、3個病房和4個衛生間的白色房子裡嗎?
So far as I know, there are many VIPs who are going to attend the reception.就我所知有很多達官貴人將出席這個招待會。
6.非限定性定語從句不用that，只用who(whose, whom)和which代表人和物;
例：Her brothers, both of whom work in America, ring her up every week.她的兄弟們，兩個人都在美國工作，每個星期都給她打電話。
The buses, most of which were already full, were surrounded by an angry crowd.那些大多已經坐滿了人的公共汽車被一群憤怒的人圍著。
That tower block, which cost five million dollars to build, has been empty for five years.那個塔樓空著已經5年了。建它花了500萬美元。
Cricket, which I know very little about, is a very popular sport in England.板球是英格蘭非常流行的體育活動，我對它知之甚少。
The accounts of the company ,which I’ve been payinggreat attention to, are in balance.公司的賬目是保持平衡的。我一直非常注意這些賬目。
7.關係副詞(=介詞+關係代詞)：
例：I shall never forget the day when (=on which) we first met.我永遠也不會忘記我們第一次見面的那一天。
The rain came at a time when (=at which) it was not needed.雨下得不是時候。
This is the computer where (=by/on which) he has stolen top-secret documents.這就是他用來盜竊絕密檔案的計算機。
Here is the place where (=at which) the murder took place.這就是謀殺發生的地方。
He didn’t give any reason why (=for which) I had been fired.他沒給任何解僱我的理由
This is the house in which (=where) my parents used to live.這就是我父母以前住過的房子
注意事項：
(1)在非正式場合， that有時可用來代替關係副詞或相當於關係副詞的“介詞+which”，而且經常全部省略，如：
In all the years that (=when/during which) I was at collage在我讀大學的那些年裡
the reason that(=why/for which)he is not happy他不高興的理由
The direction(that)(=in which )the heavenly bodies move can’t be changed.天體執行的方向是不可改變的。
He is unpopularbecause people don’t like the offensive way (that)(=in which) he talks.他不受歡迎的原因是他說話的方式讓人討厭。
(2)是用關係代詞還是用關係副詞：
關係詞(包括關係代詞和關係副詞)是學習英語定語從句的關鍵。用關係代詞還是用關係副詞，一要看關係詞在從句當中作什麼成分;二要看關係詞所代表的是人、物、時間、地點還是原因;三要看所引導的是限定性定語從句還是非限定性定語從句。所以同樣的先行詞會有不同的關係詞，這是因為關係詞在從句當中擔當的作用不同而決定的。
如：This is the room where/in which we’ll celebrate the New Year.這是我們將要在裡面慶賀新年的房間。(充當地點狀語)
This is the room(that /which)we’ll celebrate the New Year in.這是我們將要在裡面慶賀新年的房間。(充當介詞賓語，可省略。)
This is the room which /that will be used for the celebration of the New Year.這是那個將要被用來慶賀新年的房間。(充當主語)
This is the room (which/that) we’ll use for the New Year dinner party.這是我們將要用來舉行新年晚宴的房間。(充當賓語，可省略。)
The reason (that /which) he had given was not sound enough.他給的理由不夠充分。(充當賓語，可省略)
The reason why/for which he had done that was not sound enough.他做那件事的理由不夠充分。(充當原因狀語)
This is the house where she lives.這是她住的房子。
【比較：This is the house (that/which) she has bought. 這是她買的房子。This is the house that/which I’ve told you is extremely expensive.這就是我和你說過極其昂貴的那幢房子。】
I met him in the year when I was first in Xi’an.我剛到西安的那年遇到了他。
That is the reason why he did not come that morning.那就是那天上午他沒來的原因。
(3)定語從句中的時態。如果主句是一般將來時或過去將來時，從句的動作與主句的同時發生，那麼該從句要用一般現在時表示一般將來時、用一般過去時表示過去將來時。
例：Anyone who/that touches the wire will get an electric shock.任何碰這根電線的人將受到電擊。(不用will touch)
I would give her anything that she asked for.她要什麼我就給她什麼。(不用would ask)
The first person who/that opens the door will get a shock.第一個開門的'人將被嚇一跳。(不用will open)
There will be a special price for anybody who orders a suit in the next two weeks.任何人在下兩週內定做套裝都將享受優惠價格。(不用will order)
但是，如果從句和主句的動作在將來不同的時間發生，則兩部分都要用來將來時，
如：Those who will go abroad for training next year will start learning English tomorrow.那些明年出國受訓的人員，將從明天開始學習外語。
注：①先行詞有最高階形容詞修飾時，常用that，而不用which：
例：Edison was one of thegreatest inventors that ever lived.愛迪生是曾經有過的最偉大的發明家之一。
This is the best film that I’ve ever seen.這是我曾經看過的最好的電影。
She was the greatest woman that/who has ever lived.她是曾經有過的最偉大的女人。
②先行詞有the same, the very, the first, the last, all, no, the only, much, little, none, any, every等時，常用that, 而不用which：
例：He was the first man that we saw in the village.他是我們在那個村子裡看到的第一個人。
There is little that is interesting.沒什麼令人感興趣。
I still remember the first time that we met.我仍然記得我們第一次見面的時候。
I’ll do anything (that) I can to help you.我將盡一切可能幫助你。
Everything that can be done has been done.能做的一切都做了。
God bless this ship and all who sail in her.願上帝保佑此船和所有乘此船航行的人。
All that I can say is thank you very much.我能說的是(千言萬語變成一句話)：非常感謝你。
③當先行詞既有人又有物時，用that，不用which，如：
We were deeply impressed by the workers and their working conditions that we had visited.我們參觀過的工人及他們的工作條件留下了深刻印象。
We listened to him talk about the men and books that interested him.我們聽他談論他感興趣的人物和書籍。
④在same和such之後，定語從句用as引導，如：
Let’s discuss only such questions as concern us.讓我們只討論與我們有關的問題。
I’ve never heard such stories as he tells.我從來沒聽說過他講的這種故事。
I shall be surprised if he does this in the same way as I do.如果他做這件事的方法和我一樣，那就奇怪了。
She works in the same office as I do.她和我在同一個辦公室工作。
She wears the same kind of clothes as her sister does.她姐妹倆穿同樣的衣服。
He’s wearing the same dress as he wore at Mary’s wedding.他穿著與他在Mary的婚禮上穿的一樣的衣服。
This is the same watch as I have lost.這塊表和我丟的那塊一樣。
I’ve never seen such kind of people as they are.我從來沒見過像他們這樣的人。
I’ve never seen such kind people as they are.我從來沒見過象他們這樣厚道的人。
I want the same shirt as my friend’s.我要一件跟我朋友一樣的襯衫。
Such machines as are used in our workshop are made in china.我們車間使用的這種機器是中國製造的。
但是，如果從句和主句的動作在將來不同的時間發生，則兩部分都要用來將來時，
注：④在same和such之後，定語從句用as引導，偶爾，the same 後面也用that，如：
He’s wearing the same suit that he wore at Mary’s wedding.他穿著與他在Mary的婚禮上穿的一樣的衣服。
She works in the same office that I do.她和我在同一個辦公室工作。
This is the same watch that I have lost.這塊表和我丟的那塊一樣。
as 引導非限定性定語從句即可放在主句之前，也可放在主句之後，用來修飾整個句子。當as在從句中作主語時，後面常接下列句型。如：as is known, as is said, as is reported as is announced 等。例如：
As we all know, Mr. Wang is a good teacher.
As is known to all, the earth revolves round the sun.
He is tired, as you can see.
As I expected, he didn’t believe me.
As 引導非限定性定語從句時與which的區別：當主句和從句語義一致時，用as;反之，用which。如：
He made a long speech, as was expected.
He made a long speech, which was unexpected.
Tom drinks a lot every day, which his wife doesn’t like at all.
(3)但是，如果從句和主句的動作在將來不同的時間發生，則兩部分都要用來將來時，注：⑤在“介詞+關係代詞”的結構中，也可用複雜介詞，如：by means of (用，依靠)，as a result of (作為結果)等。例：
I have three children, one daughter and two sons, all of whom graduated from the same university.我有三個孩子：一個女兒、兩個兒子，他們都畢業於同一所大學。
The police, in whom I havegreat confidence, are trying to find out who did it.我對警察有極大的信心，他們正在努力尋找是誰做的這件事。
This is the part of the river in which I like to swim.(in which=where)我喜歡在這條河裡面游泳，這就是(我喜歡遊的)那個地方。
The man from whom you bought the house is my uncle.你從他那裡買下房子的那個人是我叔叔。
This is the desk by means of which he jumped over the wall.這就是他用來跳過牆去的那張桌子。
She was running a fever, as a result of which she failed in the exam.她當時正發燒，所以考試失敗了。
He is the man from whose house the picture was stolen.他就是那個家裡的畫被偷了的人。
注：⑥一個先行詞後面可以跟一個以上的定語從句，這種現象叫雙重關係從句。例：
Here are some words which are often used but which are very confusing.這裡有些常用但非常混亂的詞。
He is the only person that I can find who is able to solve the problem.他是我能找到的唯一解決這個問題的人。
