nicehost-
一、用法不同
1、who
pron. (代词)
1）who用作疑问代词时，意思是“谁”，一般只用来指人，在句中用作宾语或主语。
2）who用作限制性或非限制性的关系代词，意思是“…的人,那个…”“他，她，他们”，在句中作主语。
3）指某一组织机构的成员时也可用who，此时应用复数形式的谓语。
2、whom
pron. (代词)
1）whom是who的宾格，在正式文体中常作宾语，用作疑问代词或连接代词时非正式文体往往用主格代替，若紧跟在介词之后则只能用whom。若在从句中用作表语则只能用who，不能用whom。
2）whom用作关系代词引出定语从句修饰指人的先行词时意思是“他，她，他们”，在定语从句中作宾语，通常被省略或用who, that代替。
3）whom用于非限制性定语从句中作动词或介词的宾语时不能省略。
二、词源不同
1、who，直接源自古英语的hwa，意为谁。
2、whom，直接源自古英语的hwam，意为谁（宾格）。
三、词性不同
1、who既可以做代词也可以作连词，意思是谁。
如：Who do you think you are?
你以为你是谁？
2、whom是who的宾格形式，表示...的人。
如：I don"t know whom he has in mind for the job.
我不知道他想让谁来做这项工作。
陶小凡-
定语从句中,whom只能在从句中充当宾语成分,who既可当主语又可当宾语.但是若是介词后的宾语,只能用whom而不能用who.
如：there is nobody who/whom he can turn to for help.没有谁可以让他寻求帮助.这里引导词当宾语,who和whom都行,当然这里既可指人也可指物的that也可以。
但是：there is nobody to whom he can turn for help.这里引导词同样当宾语,但是位于介词to后,只能用whom,而不能用who（that同样不行）。
扩展资料
定语从句中易混淆的难点
1、在限定性定语从句中指代物时，which 和that 一般可通用。
The new house that/which I has just bought is about six miles away.
They planted some trees that /which did n"t need much water.
2、限定性定语从句中只用that 而不用which 的情况。A）先行词有形容词最高级修饰时 This is the best way that has been used against pollution. Polly is the most direct young woman that I have ever come across .
B) 先行词有序数词修饰时 This is the third time that they have met. The very first time that Lester saw the film, he made up his mind to become a doctor.
参考资料百度百科-定语从句
康康map-
楼主大可不必把这个东西想得那么复杂，其实很简单：Whom 只能出现在从句里面或是介词（如 to, from, at, of..）后面。
1． Whom 出现在从句里面时，所有用whom的地方都可以用who代替。Whom 这个词只出现在很正式的书面语。口语不用。
2． Whom 在介词（如 to, from, at, of..）后面时，不可替换。
Who told you the story? （主语）
Who is that man over there? （主语补语）
Whom/ Who did you meet at the airport? （宾语）
Whom did you give the book to? （介词宾语）
whom是who的宾格，在现代英语中一般只用于书面体，在口WHO 可以做主语，又可以做宾语
WHOM只能做宾语
例子：1,who are you? 不能是whom are you?
2,This book belongs to whom/who?两者都可以语中通常用who，但在介词后只能用whom。
左迁-
用作关联词的关系代词有who，whom，whose，that，which等。who，whom，whose指人，who是主格，在从句中用作主语(在非正式英语中亦可用作宾语);whom是宾格，在从句中用作宾语;whose是属格，在从句中用作定语(有时亦可指物)。如：
The man who was here yesterday is a painter. 昨天在这里的那个人是位画家。(主格关系代词who在从句中用作主语)
The man who I saw is called Smith. 我见到的那个人名叫史密斯。(在非正式英语中who 代替了whom，亦可省去不用)
I know the man whom you mean. 我认识你指的那个人。(宾语关系代词whom在从句中用作宾语)
A child whose parents are dead is called an orphan. 失去父母的孩子叫做孤儿。(属格关系代词whose在从句中用作定语，指人)
I"d like a room whose window looks out over the sea. 我想要一个窗户面临大海的房间。(属格关系代词whose在从句中用作定语，指room，可代之以of which，但后者较为正式)
that在从句中既可用作主语，亦可用作宾语(在非正式文体中可省去);既可指人，亦可指物，在当代英语中多指物。如：
A letter that is written in pencil is difficult to read. 用铅笔写的信很难读。(关系代词that在从句中用作主语，指物)
The letter that I received from him yesterday is very important. 昨天他来的信很重要。(关系代词that在从句中用作宾语，指物)
Is he the man that sells eggs? 他是卖鸡蛋的那个人吗?(关系代词that在从句中用作主语，指人)
This is the book which has been retranslated into many languages. 这就是那本有多种译本的书。(关系代词which在从句中用作主语)
Where is the book which I bought this morning? 今天上午我买的那本书在哪儿?(关系代词which在从句中用作宾语，可省去)
which在从句中亦可用作定语和表语。如：
We told him to consult the doctor, which advice he took. 我们叫他去看医生，他听取了我们的劝告。(关系代词which在从句中用作定语)
The two policemen were completely trusted, which in fact, they were. 那两个警察完全受到信任，事实上真是如此。(关系代词which在从句中用作表语)
as，than，but亦可用作关系代词。如：
The two brothers were satisfied with this decision, as was agreed beforehand. 两兄弟对这个决定都满意，它事先已经他们同意了。(关系代词as在从句中用作主语，其先行词是this decision)
He was a foreigner, as I knew from his accent. 他是个外国人，我是从他的口音知道的。(关系代词as在从句中用作宾语，其先行词是前面的整个句子)
I never heard such stories as he tells. 我从未听过他讲的这类故事。(关系代词as与指示代词such连用，在从句中用作宾语，其先行词是such stories)
Her attitude to him was quite the same as it had always been. 她对他的态度同她惯常的态度完全一样。(关系代词as与指示代词same连用，在从句中用作表语，其先行词是same)
You spent more money than was intended to be spent. 你花的钱超过了预定的数额。(关系代词than在从句中用作主语，其先行词是money)
There are very few but admire his talents. 很少人不赞赏他的才干的。(关系代词but在从句中用作主语，其先行词是few，but=who don"t)
关系代词在定语从句中用作介词宾语时，介词既可置于从句之首，亦可置于从句之末。但以置于从句之首较为正式。如：
This is the book for which you asked. 这是你所要的书。(关系代词用作介系词for宾语，放在从句之首，即which之前)
This is the book which you asked for. 这是你所要的书。(介词for置于从句之末，which在此可省去)
关系代词who和that用作介词宾语时，介词须置于句末。如：
The people who you were talking to are Swedes. 你与之谈话的那些人是瑞典人。(关系代词主格who用作介词to宾语时，介词to须置于从句之末，who在口语中可省去)
Here is the car that I told you about. 这儿就是我和你谈过的那辆汽车。(关系代词that用作介词about宾语，介词about须置于从句之末)
有时从句还有其它成分，介词则置于从句之中。如：
This is the boy who he worked with in the office. 那就是与他一道办公的那个男孩。
先行词指人时，关系代词既可用who，亦可用that。但关系代词在从句之中用作主语时，多用主格who。如：
Persons who are quarrelsome are despised. 好争吵者遭轻视。(除外persons，还有people，those，等皆多用who)
All who heard the story were amazed. 听到这个故事的人都感到吃惊。(代词如he，they，any，all，one等之后多用who)
I will pardon him who is honest. 我愿意宽恕他，他是诚实的。(描述性定语从句用who)
I think it is you who should prove to me. 我认为是你应该向我提出证据。(在强调结构中多用who，who在此可省去)
Who is not for us is against us. 谁不赞成我们就是反对我们。(缩合连接代词who为可代之以that)
在下列一些情况中则多用that。如：
He was the man that the bottle fell on. 他就是瓶子落在其身上的那个人。(此处常用that作宾语指人，亦可用whom，如果把介系词on放在从句之首，则后面的关系代词只能用whom，写成：He was the man on whom the bottle fell.)
He is a man that is never at a loss. 他是一个从未一筹莫展的人。(that常用于泛指人)
He was watching the children and parcels that filled the car. 我望着塞满车的孩子和包裹。(兼指人与物时须用that)
Who that you have ever seen can beat him in chess? 你曾见过谁能在棋艺上打败他?(避免与先行词who重复时应用that)
That"s the same man that asked for help the day before yesterday. 这个与前天求援的是同一个人。(先行词前有指示代词same时应用that)
He is not that man that he was. 他已不是过去的他了。(that常用作表语)
I knew her father for the simplest, hardest working man that ever drew the breath of life. 我早知她的父亲是一个世上最简朴最努力工作的人。(先行词前有形容词最高级、序数词或only等词时应用that)
先行词指物时，关系代词that与which往往可以互换。但在下列情况中多用that。如：
All that glitters is not gold. 闪光的东西不都是金子。(不定代词包括复合词something等只能后接that)
It was the largest map that I ever saw. 那是我所看见过的最大的地图。(前有形容词最高级等的先行词之后只能用that)
It was liberation that brought about a complete change in his life. 是解放给他的生活带来了彻底的改变。(强调结构用that)
There is a house that has bay windows. 有一栋房子有凸出的窗户。(that在此表固有的特点)
The distance that you are from home is immaterial. 你离家的距离是不足道的。(在限制性定语从句中关系代词用作表语应用that，在描述性定语从句中则应用which)
Which was the hotel that was recommended to you? 哪一个是推荐给你的旅馆?(这里用that显然是为了避免重复which)
在下列情况中则多用which。如：
Larry told her the story of the young airman which I narrated at the beginning of this book. 拉里把我在书本开关叙述过的那个关于一个青年飞行员的故事讲给她听。(离先行词较远时常用which)
A shop should keep a stock of those goods which sell best. 商店应存在最畅销的货物。(“those+复形名词”之后多用which)
I have that which you gave me. 我有你给我的那个。(which比较正式，在非正式英语中也可用that)
Beijing, which was China"s capital for more than 800 years, is rich in cultural and historic relics. 北京曾是八百多年的中国首都，有很丰富的历史文物。(描述性定语从句一般皆用which)
This is the one of which I"m speaking. 这就是我所讲的那个。(介系词之后须用which)
再也不做稀饭了-
定语从句及相关术语
1.定语从句：修饰一个名词或代词的从句称为定语从句，一般紧跟在它所修饰的先行词后面。2.关系词：引导定语从句的关联词成为关系词关系词有关系代词和关系副词。关系代词有that, which, who, whom, whose, as等；关系副词有where, when, why等。关系词常有3个作用：1，引导定语从句。2，代替先行词。3，在定语从句中担当一个成分。
（序）
1 定语可以由形容词，名词，代词，数词，分词，副词，不定式以及介词短语来担任，也可以由一个句子来担任．
定语从句是由关系代词或关系副词引导的从句，其作用是作定语修饰主句的某个名词性成分，相当于形容词，所以又称为形容词性从句．
2 定语从句用来修饰名词，代词或整个主句．
3 定语从句分为限定性和非限定性从句两种。
4 定语从句存在的条件:先行词+关系词（有的版本作关联词）+从句
（一） 限定性定语从句
1. that即可代表事物也可代表人，which代表事物；它们在从句中作主语或宾语，that在从句中作宾语时常可省略关系词，which在从句中作宾语则不能省略。而且，如果which在从句中作“不及物动词＋介词”的介词的宾语，注意介词不要丢掉，而且介词总是放在关系代词which的前边，但有的则放在它原来的位置
2. which作宾语时，根据先行词与定语从句之间的语义关系，先行词与which之间的介词不能丢
3. 代表物时多用which，但在带有下列词的句子中用that而不用which，这些词包括all, anything, much等，这时的that常被省略
4. who和whom引导的从句用来修饰人，分别作从句中的主语和宾语，whom作宾语时，要注意它可以作动词的宾语也可以作介词的宾语
5. where是关系副词，用来表示地点的定语从句
6. when引导定语从句表示时间〔注〕值得一提的是，表示时间“time"一词的定语从句只用when引导，有时不用任何关系代词，当然也不用that引导
By the time you arrive in London, we will have stayed there for two weeks. I still remember the first time I met her. Each time he goes to business trip, he brings a lot of living necessities, such as towers, soap, toothbrush etc.
7. whose是关系代词，修饰名词作定语，相当于所修饰成分的前置所有格
8. 当从句的逻辑主语是some, any, no, somebody, anybody, nobody, something, anything, everything或nothing时，常用there is来引导
（二）非限定性定语从句
非限定性定语从句的作用是对所修饰的成分作进一步说明，通常是引导词和先行词之间用逗号隔开，将从句拿掉后其他部分仍可成立
1. which引导的非限定性定语从句来说明前面整个句子的情况或主句的某一部分
2. 在引导限定性定语从句时，that有时相当于in which, at which, for which或at which
Attitudes towards daydreaming are changing in much the same way that(in which) attitudes towards night dreaming have changed.
人们对白日做梦的态度正在改变，这与人们对夜间做梦的看法的变化有非常相似之处。
I like the music for the very reason that(for which) he dislike it.
我出于某种原因喜欢这种音乐，而他恰恰与我相反。
We arrived the day that(on which) they left.
刚好我们到的那天他们走了。
3. 有时as也可用作关系代词
4. 在非限定性定语从句中，不能用that，而用who, whom代表人，用which代表事物.
（三）关系代词引导的定语从句
1.who指人，在从句中做主语
(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，在定语从句中充当宾语，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：关系代词whom在口语和非正式语体中常用who代替，可省略。
(3) The man who/whom you met just now is my friend
3.which指物，在定语从句中做主语或者宾语，做宾语时可省略
(1) Football is a game which is liked by most boys.
(2) This is the pen (which) he bought yesterday.
如果在从句中做宾语,就用whom或who.比如: He is the man whom/who I talk to.
如果是在从句中作主语就只能用who.比如: He is the man who has an English book.
4. that指人时，相当于who或者whom；指物时，相当于which。
在定语从句中做主语或者宾语，做宾语时可省略。
(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，在定语从句中做定语
(1) He has a friend whose father is a doctor.
(2) I once lived in a house whose roof has fallen in.whose指物时，常用以下结构来代替
(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?
（四）注意
介词+关系代词引导的定语从句关系代词在定语从句中做介词宾语时
从句常由介词+关系代词引导
(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. 含有介词的动词短语一般不拆开使用，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. 若介词放在关系代词前，关系代词指人时用whom，不可用who或者that；指物时用which，不能用that；关系代词是所有格时用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. “介词+关系代词”前可有some, any, none, both, all, neither, most, each, few等代词或者数词
(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.
（五）关系副词引导的定语从句
1. when指时间，在定语从句中做时间状语
(1) I still remember the day when I first came to the school.
(2) The time when we got together finally came.2. where指地点，在定语从句中做地点状语
(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，在定语从句中做原因状语
(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：关系副词引导的从句可以由“介词+关系代词”引导的从句替换
(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.
（六）判断关系代词与关系副词
方法一： 用关系代词，还是关系副词完全取决于从句中的谓语动词。及物动词后面无宾语，就必须要求用关系代词；而不及物动词则要求用关系副词。例如：
This is the mountain village where I stayed last year.
I"ll never forget the days when I worked together with you.
判断改错（注：先显示题，再显示答案，横线；用不同的颜色表示出。）
（错） This is the mountain village where I visited last year.
（错） I will never forget the days when I spent in the countryside.
（对） This is the mountain village (which) I visited last year.
（对） I"ll never forget the days (which) I spent in the countryside.
习惯上总把表地点或时间的名词与关系副词 where, when联系在一起。此两题错在关系词的误用上。
方法二： 准确判断先行词在定语从句中的成分(主、谓、宾、定、状)，也能正确选择出关系代词/关系副词。例1. Is this museum ___ you visited a few days age?
A. where B. that C. on which D. the one
例2. Is this the museum ____ the exhibition was held.
A. where B. that C. on which D. the one答案：
例1 D，例2 A
例1变为肯定句： This museum is ___ you visited a few days ago.例2变为肯定句： This is the museum ___ the exhibition was held.
在句1中，所缺部分为宾语，而where, that, on which都不能起到宾语的作用，只有the one既做了主句的表语，又可做从句的宾语，可以省略关系代词，所以应选D。
而句2中, 主、谓、宾俱全，从句部分为句子的状语表地点，既可用副词where，又因 in the museum词组，可用介词in + which 引导地点状语。而此题中，介词on 用的不对，所以选A。
关系词的选择依据在从句中所做的成分，先行词在从句中做主、定、宾语时，选择关系代词 (who, whom, that, which, whose)；
先行词在从句中做状语时，应选择关系副词 ( where 地点状语，when 时间状语，why 原因状语) 。
（七）介词+关系词
1）介词后面的关系词不能省略。
2）that前不能有介词。
3） 某些在从句中充当时间，地点或原因状语的"介词+关系词"结构可以同关系副词when 和where 互换。 This is the house in which I lived two years ago.
This is the house where I lived two years ago.
Do you remember the day on which you joined our club?
Do you remember the day when you joined our club?
（八）先行词和关系词二合一
1)Whoever spits in public will be punished here. (Whoever 可以用 anyone who 代替) 2)The parents will use what they have to send their son to technical school. (what 可以用all that代替)
（九as） which 非限定性定语从句
由as, which 引导的非限定性定语从句，as和which可代整个主句，相当于and this或and that。As一般放在句首，which在句中。
As we know, smoking is harmful to one"s health.
The sun heats the earth, which is very important to us.
典型例题
1）Alice received an invitation from her boss, ___came as a surprise.
A. it B. that C. which D. he
答案C. 此为非限定性从句，不能用 that修饰，而用which.，it 和he 都使后句成为句子，两个独立的句子不能单以逗号连接。况且选he句意不通。
2）The weather turned out to be very good, ___ was more than we could expect.
A. what B. which C. that D. it
答案B。
which可代替句子，用于非限定性定语从句，而what不可。That 不能用于非限定性定语从句，it不为连词，使由逗号连接的两个句子并在一起在英语语法上行不通。
3）It rained hard yesterday, ____ prevented me from going to the park..
A. that B. which C. as D. it
答案B.
as 和which在引导非限制性定语从句时，这两个关系代词都指主句所表达的整个意思，且在定语从句中都可以作主语和宾语。但不同之处主要有两点：
(1） as 引导的定语从句可置于句首，而which不可。
(2） as 代表前面的整个主句并在从句中作主语时，从句中的谓语必须是系动词；若为行为动词，则从句中的关系代词只能用which.。
在本题中，prevent由于是行为动词，所以正确选项应为B。
As 的用法例
1. the same… as；such…as 中的as 是一种固定结构, 和……一样……。
I have got into the same trouble as he (has).
例2. as可引导非限制性从句，常带有"正如"。
As we know, smoking is harmful to one"s health.
As is know, smoking is harmful to one"s health.
As是关系代词。例1中的as作know的宾语；
例2中，它充当从句的主语，谓语动词know要用被动式。
（十）关系代词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.
We depend on the land that/which we get our food from.
(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,the same,the last,just修饰时，只用that。
(d) 先行词为序数词、数词、形容词最高级时，只用that。.
(e) 先行词既有人，又有物时。
(f) 先行词指物，在主句中作表语时．
(g) 为了避免重复．
(h)先行词是the way时
举例：
Is this the book that you borrowed in the library?
这是你在图书馆借的那本书吗？
Who that break the window should be punished．
谁打碎了窗户都要受到惩罚．
All that is needed is a supply of oil.
所需的只是供油问题。
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。
（十一）难点分析
（一）限制性定语从句只能用that的几种情况
1．当先行词是anything, everything, nothing (something 除外), few, all, none, little, some等代词时，或者是由every, any, all, some, no, little, few, much等修饰时
(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：当先行词指人时，偶尔也可以用who
(4) Any man that/.who has a sense of duty won"t do such a thing.
2. 当先行词被序数词修饰
(1) The first place that they visited in London was the Big Ben.
3. 当先行词被形容词最高级修饰时
(1) This is the best film that I have seen.
4. 当形容词被the very, the only 修饰时
(1) This is the very good dictionary that I want to buy,
(2) After the fire in his house, the old car is the only thing that he owned.
当先行词指人时，偶尔也可以用who
(3) Wang Hua is the only person in our school who will attend the meeting？
5. 当先行词前面有who, which等疑问代词时
(1) Who is the man that is standing there?
(2) Which is the T-shirt that fits me most?
6. 当先行词既有人，也有动物或者物体时
(1) Can you remember the scientist and his theory that we have learned?
（二）关系代词as和which引导的定语从句as和which引导非限制性定语从句，有相同之处也有不同之处。具体情况是：
1．As和which都可以在定语从句中做主语或者宾语，代表前面整个句子。
(1) He married her, as/which was natural.
(2) He was honest, as/which we can see.
2. as 引导非限制性定语从句，可放在主句之前，或者主句之后，甚至可以切割一个主句；which引导的非限制性定语从句只能放在主句之后。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：当主句和从句存在逻辑上的因果关系时，常用which
(5) Tom was always late for school, which made his teacher angry.
3. 当先行次受such, the same修饰时，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：当先行词由the same修饰时，偶尔也用that引导定语从句，但是和由as所引导的定语从句意思不同
(4) She wore the same dress that she wore at Mary"s wedding.
她穿着她在MARY婚礼上穿过的一条裙子。
(5) She wore the same dress as her young sister wore. 她穿着和她妹妹所穿的一样的裙子。
(三）以the way为先行词的定语从句通常由in which, that引导，而且通常可以省略。
(1) The way in which/ that/./ he answered the question was surprising.
(四) but有时也可以做关系词引导定语从句
(1) There are very few but understand his idea.
( but= who don"t )
(五) 区分定语从句和同位语从句
1．定语从句修饰先行词，它和先行词是修饰关系；
同位语从句说明先行词的具体内容，是补充说明的关系
(1) The plane that has just taken off is for London. 定语从句
(2) The fact that he has been dead is clear. 同位语从句
2．定语从句由关系代词或者关系副词引导，关系词在句中充当成分，有时可以省略；
同位语从句主要由that引导，在句中一般不做成分；
句子也可以由when, where, how, why, whether, what等词引导，充当成分
(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. 定语
(4) The problem how we can collect so much money is difficult to solve.
3. 同位语从句和先行词一般可以用be动词发展成一个完整的句子，而定语从句不可以
(1) The idea that we could ask the teacher for advice is wonderful. 同位语
(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.
(4) The fact is that the earth moves around the earth.
余辉-
定语从句中关系代词who在95%的情况下在定语从句中充当主语，而whom则充当从句中的宾语（包括动词宾语和介词宾语）。需要了解的是who在5%的情况下在定语从句中可以充当宾语（这一点湖南高考2010中考过）
Is he the man who/that wants to see you? 他是那个男人想见你？（who/that在从句中作主语）
He is the man whom/ that I saw yesterday. 他就是我昨天见的那个人。（whom/that在从句中作宾语）
snjk-
WHO 是主格，WHOM是宾格
e.g Who will go to the theatre with you?
With whom will you go to the theatre?
楼上的解释是对的，我补充一点 whom did you give the pen to？ 这一句句首用Who 也行，但是当to提前时就只能用whom
Who did you give the pen to? To whom did you give the pen?
LuckySXyd-
1、例：Do you know the person who talked to me
此时，先行词在从句中作主语成分，只能用who,而不能用whom
2、例：He is one of the students to whom i have talked
当介词提前，介词后必须用且只能用whom
3、例：Gina ,who lives in China is my friend.
当定语从句为非限制性定语从句时，只能用who。
4、例：Do you know the person whomwho省略不写 i talked to
当先行词在从句中作宾语成分时，whom who 都可以，也可以省略不写。
瑞瑞爱吃桃-
1、who 可以做主语,又可以做宾语； whom只能做宾语 。
2、who指人,在从句中做主语 ；whom指人,在定语从句中充当宾语,常可省略。
3、关系代词whom在口语和非正式语体中常用who代替,可省略。
【扩展资料】：
(1) The boys who are playing football are from Class One.
(2) Yesterday I helped an old man who lost his way.
(3) Mr.Liu is the person (whom) you talked about on the bus.
(4) Mr.Ling is just the boy whom I want to see.
可可-
who 是做主语成分 后面接动词
如 who did it?
whom 是做宾语成分 动作的对象
如 whom did you give the pen to
如果改成祈使句就很明白
you gave the pen to whom( 宾语）