定语从句专项笔记总结
定语从句是由关系代词或关系副词引导的修饰名词或代词的从句，是一种形容词性的从句。
被修饰的名词或代词叫先行词。
1． 关系代词：who whom whose which that
关系代词引导从句，代替先行词，在从句中充当一个成分，如：主语、宾语、定语等， 所以在作主语时，动词的数要和先行词的数保持一致。
who----可作主语、宾语，作主语时，只能用who, who作宾语时是非正式
This is the man who helped me.
whom---作宾语（正式用法），在介词后只能用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的属格形式，用来指人，也可以用来指物
that--- 可代替who ,whom
Which----可作主语，宾语
物 eg. The watch which was lost has been found.
eg. The fish (which) we bought were not fresh
that-------可作主语，宾语
eg. The letter that I receive was from my father.
当关系代词充当介词宾语时，可以把介词提前，也可以不提前，但是在含有介词的动词固定搭配中，介词只能放在原来的位置
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词组中for不能提前)
先行词是人时，常用who而不用that 的情况：
a. 关系代词在从句中作主语时，多用who，
eg. I will pardon him who is honest.
b. 先行词为 all one ones anyone those 等时，
eg. All who heard the news were excited.
c. 在以there be 开头的句子中，
eg. There is a girl who wants to see you.
d. 当先行词后有较长的修饰语时，
eg. He met a boy in the street yesterday who could speak English fluently.
先行词指物的特殊情况：
1． 必须用that的情况：
a. 先行词被序数词、形容词的最高级修饰时，
eg. This is the first job that I have taken up.
This is the most interesting novel that I have ever read.
b. 先行词是不定代词,something somebody nothing anything 等 或是 all little much 时，
eg. There is something that I want to tell you.
c. 先行词被all any every each few little no some much only none both either neither 等修饰时，
eg. I have read all the books that you lent me.
d. 先行词被the only, the last, the very…修饰时,
eg. This is the only method we can use.
e. 先行词又有人又有物时，
eg. They talked about things and persons that they know in the school.
f. 主句以who 或which开头时，
eg. Who is the old man that speak to you just now ?
g. 先行词指物时，且在There be 句型引导的定语从句中，
eg. There is a house that has three windows.
h. 关系代词作表语时，
eg. China is no longer the place that it used to be.
2. 必须用which 的情况：
a. 个非限制性定语从句，
b. 句子末尾的介词提前时，只能用which,
c. 关系代词后有插入语时,
eg. This is the book which, as I have told you, will help you to improve your English.
（这就是我跟你说过的，能帮你学好英语的那本书。）
关于as 引导的定语从句，as可以在限制性或非限制性定语从句中主语或宾语
1． 在限制性定语从句中，as多和such, the same 连用，
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. 非限制性定语从句中，as 所指的是它前面的整个主句，
eg. Tom was admitted into the University, as we had hoped.
as 和which 在代替主语时的区别：
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 没有