學生在學習過程中，常會遇到as作為關系代詞出現，學生對as定語從句多有疑惑，如下是小編給大家整理的定語從句as的用法總結，希望對大家有所作用。
(1) as引導的定語從句修飾表人或物的先行詞，即先行詞可以是人也可以是物；在定語從句中可以做主語、賓語或表語；常用于the sameas/suchas/as(so)as句型，as不論在定語從句中作何成分，均不能省略。
① 先行詞為人such teachers， as作主語
②I’ll buy the same bike as I lost yesterday. 先行詞為物the same bike，as作賓語 ,指同一類事物 ※此時注意和the same that 引導的定語從句的區別
It’ that引導定語從句，作賓語，指同一個事物
※ She wore the same dress that she wore at Marys wedding. (the samethat特指同一個) 她穿著她在Mary婚禮上穿過的同一條裙子。 (the sameas 泛指同一類) 她穿著和她妹妹所穿的一樣的裙子。 那塊手表和我丟失的一模一樣。(the sameas 泛指同一類) 那就是我丟失的那塊手表。(the samethat特指同一個) ③The school is just the same one as it was 10 years ago.
先行詞為物the same one (school), as作表語
It’ 先行詞為物so heavy a box，as作賓語
此時應注意as引導的定語從句和結果狀語從句such / sothat的區分
It’ 結果狀語從句sothat如此以至于 ※He is such a good student as is liked by everyone.(定語從句，as在從句中作主語) （結果狀語從句suchthat） that在從句中不充當任何成分，故不是定語從句，而是結果狀語從句
(2) as引導的非限制性定語從句可以修飾整個主句, 可以放在主句前，主句后或插入主句中間。此時as含有“正如” 之意。常用的as引導的.非限制性定語從句固定表達有：
as we all know / as everyone knows / as is known to all / as is well-known (眾所周知)/ as I can remember(正如我所記得的) / as we expect / as was expected (正如預料的那樣)/ as often happens / as we all can see / as can be seen / as has been said before (如前所述)…
As everyone knows, Shakespeare is a famous writer.
Shakespeare is a famous writer, as everyone knows.
Shakespeare, as everyone knows , is a famous writer.
(3)注意which引導的非限制性定語從句也可以修飾整個主句, 但不能放在主句前，常譯為“這一點、這件事”。
She is working hard, which everyone can see.which引導的非限制性定語從句不能放在主句前 She is working hard, as everyone can see.﹦As everyone can see, She is working hard.
(4)注意當修飾整個主句時，as引導的非限制性定語從句含“正如”之意，因此在意義上不能和主句相抵觸；which引導的非限制性定語從句則無此限制。如： 我們的球隊輸了比賽，這一點是未預料到的。此時不能用as。我們的球隊贏了比賽，正如預料的那樣。
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