一.定語從句及相關術語
1.定語從句：修飾一個名詞或代詞的從句稱爲定語從句，一般緊跟在它所修飾的先行詞後面。
2.關係詞：引導定語從句的關聯詞成爲關係詞 關係詞有關係代詞和關係副詞。
關係代詞有that, which, who, whom, whose, as 等；
關係副詞有where, when, why等。 關係詞常有3個作用;
1，引導定語從句。2，代替先行詞。3，在定語從句中擔當一個成分。
二.關係代詞引導的定語從句
1.who指人，在從句中做主語
(1) The boys who are playing football are from Class One.
(2) Yesterday I helped an old man who lost his way.
2. whom指人，在定語從句中充當賓語，常可省略。
(1) Mr. Liu is the person (whom) you talked about on the bus.
(2) Mr. Ling is just the boy whom I want to see.
注意：關係代詞whom在口語和非正式語體中常用who代替，可省略。
(3) The man who/whom you met just now is my friend.
3. which指物，在定語從句中做主語或者賓語，做賓語時可省略
(1) Football is a game which is liked by most boys.
(2) This is the pen (which) he bought yesterday.
4. that指人時，相當於who 或者whom；指物時，相當於which。在賓語從句中做主語或者賓語，做賓語時可省略。
(5) The number of the people that/who come to visit the city each year rises one million.
(6) Where is the man that/whom I saw this morning?
5. whose通常指人，也可指物，在定語從句中做定語
(1) He has a friend whose father is a doctor.
(2) I once lived in a house whose roof has fallen in.
whose指物時，常用以下結構來代替
(3) The classroom whose door is broken will soon be repaired.
(4) The classroom the door of which is broken will soon be repaired.
(5) Do you like the book whose cover is yellow?
(6) Do you like the book the color of which is yellow?
三.介詞+關係代詞引導的定語從句,關係代詞在定語從句中做介詞賓語時，從句常由介詞+關係代詞引導
(1) The school (that/which) he once studied in is very famous.
(2) The school in which he once studied is very famous.
(3) Tomorrow I will bring here a magazine (that/which) you asked for.
(4) Tomorrow I will bring here a magazine for which you asked.
(5) We'll go to hear the famous singer (whom/that/who) we have often talked about.
(6) We'll go to hear the famous singer about whom we have often talked.
注意：
1. 含有介詞的動詞短語一般不拆開使用，如：look for, look after, take care of等
(1) This is the watch which/that I am looking for. (T)
(2) This is the watch for which I am looking. (F)
2.若介詞放在關係代詞前，關係代詞指人時用whom，不可用who或者that；指物時用which，不能用that；
關係代詞是所有格時用whose
(1) The man with whom you talked is my friend. (T)
(2) The man who/that you talked with is my friend. (F)
(3) The plane in which we flew to Canada is very comfortable. (T)
(4) The plane in that we flew in to Canada is very comfortable. (F)
3.“介詞+關係代詞”前可有some, any, none, both, all, neither, most, each, few等代詞或者數詞
(1) He loved his parents deeply, both of whom are very kind to him.
(2) In the basket there are quite many apples, some of which have gone bad.
(3) There are forty students in our class in all, most of whom are from big cities.
四．關係副詞引導的定語從句
1. when指時間，在定語從句中做時間狀語
(1) I still remember the day when I first came to the school.
(2) The time when we got together finally came.
2. where指地點，在定語從句中做地點狀語
(1) Shanghai is the city where I was born.
(2) The house where I lived ten years ago has been pulled down.
3. why指原因，在定語從句中做原因狀語
(1) Please tell me the reason why you missed the plane.
(2) I don't know the reason why he looks unhappy today.
注意：關係副詞引導的從句可以由“介詞+關係代詞”引導的從句替換
(1) The reason why/ for which he refused the invitation is not clear,
(2) From the year when/in which he was going to school he began to know what he wanted when he grew up.
(3) Great changes have taken place in the city in which/where I was born.
五．限制性定語從句和非限制性定語從句 限制性定語從句舉例：
(1) The teacher told me that Tom was the only person that I could depend on.
(2) China is a country which has a long history.
非限制性定語從句舉例：
(1) His mother, who loves him very much, is strict with him.
(2) China, which was founded in 1949, is becoming more and more powerful.
要注意區分以下幾個句子的不同
(1) His brother who is now a doctor always encourages him to go to college.
他那當醫生的哥哥常鼓勵他要考上大學。（他還有其他的哥哥）
(2) His brother, who is now a doctor, always encourages him to go to college.
他的哥哥是當醫生的，常鼓勵他要考上大學。（他只有一個哥哥）
難點分析 （
一）限制性定語從句只能用that 的幾種情況
1.當先行詞是anything, everything, nothing (something 除外), few, all, none, little, some 等代詞時，
或者是由every, any, all, some, no, little, few, much 等修飾時
(1) Have you taken down everything that Mr. Li has said?
(2) There seems to be nothing that seems impossible for him in the world.
(3) All that can be done has been done. (4) There is little that I can do for you.
注意：當先行詞指人時，偶爾也可以用who
(4) Any man that/.who has a sense of duty won't do such a thing.
2. 當先行詞被序數詞修飾
(1) The first place that they visited in London was the Big Ben.
3. 當先行詞被形容詞最高級修飾時
(1) This is the best film that I have seen.
4. 當形容詞被the very, the only修飾時
(1) This is the very dictionary that I want to buy,
(2) After the fire in his house, the old car is the only thing that he owned.
當先行詞指人時，偶爾也可以用who
(3) Wang Hua is the only person in our school who will attend the meeting.
5. 當先行詞前面有who, which等疑問代詞時
(1) Who is the man that is standing there?
(2) Which is the T-shirt that fits me most?
6. 當先行詞既有人，也有動物或者物體時
(1) Can you remember the scientist and his theory that we have learned?
（二）關係代詞as和which 引導的定語從句 as和which引導非限制性定語從句，有相同之處也有不同之處。
具體情況是：
1．As和which都可以在定語從句中做主語或者賓語，代表前面整個句子。
(1) He married her, as/which was natural.
(2) He was honest, as/which we can see.
2. as引導非限制性定語從句，可放在主句之前，或者主句之後，甚至可以切割一個主句；
which引導的非限制性定語從句只能放在主句之後。另外，as有“正如……，正像……”的意思
(1) As is known to all, China is a developing country.
(2) He is from the south, as we can see from his accent.
(3) John, as you know, is a famous writer.
(4) He has been to Paris more than several times, which I don't believe.
注意：當主句和從句存在邏輯上的因果關係時，常用which
(5) Tom was always late for school, which made his teacher angry.
3. 當先行次受such, the same修飾時，常用as
(1) I have never heard such a story as he tells.
(2) He is not such a fool as he looks.
(3) This is the same book as I lost last week.
注意：當先行次由the same修飾時，偶爾也用that引導定語從句，但是和由as 所引導的定語從句意思不同
(4) She wore the same dress that she wore at Mary's wedding.
她穿着她在Mary婚禮上穿過的一條裙子。
(5) She wore the same dress as her young sister wore.
她穿着和她妹妹所穿的一樣的裙子。
（三）以the way爲先行詞的定語從句通常由in which, that引導，而且通常可以省略。
(1) The way in which/ that/./ he answered the question was surprising.
(四) but 有時也可以做關係詞引導定語從句
(1) There are very few but understand his idea. ( but= who don't )
(五)區分定語從句和同位語從句
1．定語從句修飾先行詞，它和先行詞是修飾關係；同位語從句說明先行詞的具體內容，是補充說明的關係
(1) The plane that has just taken off is for London. 定語從句
(2) The fact that he has been dead is clear. 同位於從句
2．定語從句由關係代詞或者關係副詞引導，關係詞在句中充當成分，有時可以省略；
同位語從句主要由that引導，在句中一般不做成分；句子也可以由when, where, how, why, whether, what等詞引導，充當成分
(1) The news he told me is true.
(2) The news that he has just died is true.
(3) The problem that we are facing now is how we can collect so much money. 定語
(4) The problem how we can collect so much money is difficult to solve.
3. 同位語從句和先行詞一般可以用be動詞發展成一個完整的句子，而定語從句不可以
(1) The idea that we could ask the teacher for advice is wonderful.
(2) The idea was that we could ask the teacher for advice.
(3) The fact that the earth moves around the earth is known to all. 同位語
(4) The fact is that the earth moves around the earth.