引導語：定語從句起了形容詞的作用，在句中修飾一個名詞或代詞。被修飾的`詞叫做先行詞，引導定語從句的詞叫關係詞，他的作用一是放在先行詞與定語從句中間起了連接作用，二是在從句中擔當一個成分，並與先行詞保持數的一致。
關係代 詞
who
人
主語
Do you know the man who is talking with your mother?
whom, which和that在從句中做賓語時，常可以省略，但介詞提前時後面關係代詞不能省略，也不可以用that
whom
人
賓語
Mr. Smith is the person with whom I am working
The boy (whom) she loved died in the war..
whose
人或物
定語
I like those books whose topics are about history.
The boy whose father works abroad is my deskmate.
that
人或物
主語，賓語
A plane is a machine that can fly.
She is the pop star (that) I want to see very much.
which
物
主語，賓語
The book (which) I gave you was worth $10.
The picture which was about the accident was terrible.
as
人或物
主語，賓語
He is such a person as is respected by all of us.
This is the same pen as I lost yesterday.
as做賓語一般不省略
關係副 詞
when
時間
時間狀語
I will never forget the day when we met there.
可用on which
where
地點
地點狀語
This is the house where I was born.
可用in which
why
原因
原因狀語
I can’t imagine the reason why he turned down my offer.
可用for which
II. that與which, who, whom的用法區別
只用that的情況
1.先行詞爲all, everything, anything, nothing, little, much,等不定代詞時
2.先行詞被all, any, every, each, much, little, no, some, few等修飾時
3.先行詞有形容詞最高級和序數詞修飾時
4.先行詞既指人又指物時
5.先行詞被the only, the very修飾時
6.句中已經有who或which時，爲了避免重複時
told me everything that he knows.
the books that you offered has been given out.
is the best film that I have ever read.
talked about the persons and things that we remembered.
is the only man that I want to see.
is the man that is making a speech?
只用which, who, whom的情況
1.在非限制性定語從句中，只能用which指代物，用who/whom指人
2.在由“介詞+關係代詞”引導的定語從句中，只能用which指物，whom指人。
3.先行詞本身是that時，關係詞用which, 先行詞爲those, one, he時多用who。
has a son, who has gone abroad for further study.
2.I like the person to whom the teacher is talking.
e who respect others are usually respected by others.
III. as、which和that的區別
限制性
定語從句中
名詞前有such和the same修飾時，關係代詞用as,不能用which
He is not such a fool as he looks.
Don’t read such books as you can’t understand.
非限制性
定語從句中
as和which都可以指代前面整個主句。如果有“正如，象”的含義，並可以放在主句前，也可以放在後面，那麼用as；而which引導的從句只能放主句後，並無“正如”的意思。
They won the game, as we had expected.
They won the game, which we hadn’t expected.
As is well known, he is a famous film star in the 1980s.
the same... as和
the same
the same... as指同類事物
the same 指原物
That’s the same tool as I used last week.（同類工具，不是同一把）
That’s the same tool that I used last week.那就是我上週用過的工具。
注意：the way 做先行詞時，定語從句可由that, in which 引導或不用引導詞。
