学生在学习过程中，常会遇到as作为关系代词出现，学生对as定语从句多有疑惑，如下是小编给大家整理的定语从句as的用法总结，希望对大家有所作用。
(1) as引导的定语从句修饰表人或物的先行词，即先行词可以是人也可以是物；在定语从句中可以做主语、宾语或表语；常用于the sameas/suchas/as(so)as句型，as不论在定语从句中作何成分，均不能省略。
① 先行词为人such teachers， as作主语
②I’ll buy the same bike as I lost yesterday. 先行词为物the same bike，as作宾语 ,指同一类事物 ※此时注意和the same that 引导的定语从句的区别
It’ that引导定语从句，作宾语，指同一个事物
※ She wore the same dress that she wore at Marys wedding. (the samethat特指同一个) 她穿着她在Mary婚礼上穿过的同一条裙子。 (the sameas 泛指同一类) 她穿着和她妹妹所穿的一样的裙子。 那块手表和我丢失的一模一样。(the sameas 泛指同一类) 那就是我丢失的那块手表。(the samethat特指同一个) ③The school is just the same one as it was 10 years ago.
先行词为物the same one (school), as作表语
It’ 先行词为物so heavy a box，as作宾语
此时应注意as引导的定语从句和结果状语从句such / sothat的区分
It’ 结果状语从句sothat如此以至于 ※He is such a good student as is liked by everyone.(定语从句，as在从句中作主语) （结果状语从句suchthat） that在从句中不充当任何成分，故不是定语从句，而是结果状语从句
(2) as引导的非限制性定语从句可以修饰整个主句, 可以放在主句前，主句后或插入主句中间。此时as含有“正如” 之意。常用的as引导的.非限制性定语从句固定表达有：
as we all know / as everyone knows / as is known to all / as is well-known (众所周知)/ as I can remember(正如我所记得的) / as we expect / as was expected (正如预料的那样)/ 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引导的非限制性定语从句也可以修饰整个主句, 但不能放在主句前，常译为“这一点、这件事”。
She is working hard, which everyone can see.which引导的非限制性定语从句不能放在主句前 She is working hard, as everyone can see.﹦As everyone can see, She is working hard.
(4)注意当修饰整个主句时，as引导的非限制性定语从句含“正如”之意，因此在意义上不能和主句相抵触；which引导的非限制性定语从句则无此限制。如： 我们的球队输了比赛，这一点是未预料到的。此时不能用as。我们的球队赢了比赛，正如预料的那样。
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