定語從句專項筆記總結
定語從句是由關系代詞或關系副詞引導的修飾名詞或代詞的從句，是一種形容詞性的從句。
被修飾的名詞或代詞叫先行詞。
1． 關系代詞：who whom whose which that
關系代詞引導從句，代替先行詞，在從句中充當一個成分，如：主語、賓語、定語等， 所以在作主語時，動詞的數要和先行詞的數保持一致。
who----可作主語、賓語，作主語時，只能用who, who作賓語時是非正式
This is the man who helped me.
whom---作賓語（正式用法），在介詞后只能用whom
人 This is the man whom I met in the street yesterday. (正式用法)
This is the man who I met in the street yesterday. (非正式用法)
whose-who的屬格形式，用來指人，也可以用來指物
that--- 可代替who ,whom
Which----可作主語，賓語
物 eg. The watch which was lost has been found.
eg. The fish (which) we bought were not fresh
that-------可作主語，賓語
eg. The letter that I receive was from my father.
當關系代詞充當介詞賓語時，可以把介詞提前，也可以不提前，但是在含有介詞的動詞固定搭配中，介詞只能放在原來的位置
eg. This is the teacher whom he worked with .
This is the teacher with whom he worked .
eg. This is the book for which you asked.
This is the book which you asked for.
eg. This is the pen which he has been looking for. (look for詞組中for不能提前)
先行詞是人時，常用who而不用that 的情況：
a. 關系代詞在從句中作主語時，多用who，
eg. I will pardon him who is honest.
b. 先行詞為 all one ones anyone those 等時，
eg. All who heard the news were excited.
c. 在以there be 開頭的句子中，
eg. There is a girl who wants to see you.
d. 當先行詞后有較長的修飾語時，
eg. He met a boy in the street yesterday who could speak English fluently.
先行詞指物的特殊情況：
1． 必須用that的情況：
a. 先行詞被序數詞、形容詞的最高級修飾時，
eg. This is the first job that I have taken up.
This is the most interesting novel that I have ever read.
b. 先行詞是不定代詞,something somebody nothing anything 等 或是 all little much 時，
eg. There is something that I want to tell you.
c. 先行詞被all any every each few little no some much only none both either neither 等修飾時，
eg. I have read all the books that you lent me.
d. 先行詞被the only, the last, the very…修飾時,
eg. This is the only method we can use.
e. 先行詞又有人又有物時，
eg. They talked about things and persons that they know in the school.
f. 主句以who 或which開頭時，
eg. Who is the old man that speak to you just now ?
g. 先行詞指物時，且在There be 句型引導的定語從句中，
eg. There is a house that has three windows.
h. 關系代詞作表語時，
eg. China is no longer the place that it used to be.
2. 必須用which 的情況：
a. 個非限制性定語從句，
b. 句子末尾的介詞提前時，只能用which,
c. 關系代詞后有插入語時,
eg. This is the book which, as I have told you, will help you to improve your English.
（這就是我跟你說過的，能幫你學好英語的那本書。）
關于as 引導的定語從句，as可以在限制性或非限制性定語從句中主語或賓語
1． 在限制性定語從句中，as多和such, the same 連用，
eg. He told me his experience such ad I had never had before.
I should like to use the same tool as is used here.
2. 非限制性定語從句中，as 所指的是它前面的整個主句，
eg. Tom was admitted into the University, as we had hoped.
as 和which 在代替主語時的區別：
a. as 可以提到句首，但是which 不可以，
b. as 有“正如…，就像…”的意思，但是which 沒有