定語從句中as和which的區別

一、在限制性定語從句中

在such或 the same之后常用as 作為關系代詞引導定語從句，不用which。

such， the same與as 搭配使用，as充當定語從句的主語或賓語。

1.Have you read such a book as I bought yesterday? (as作賓語)

2.Such tourists as know Guilin think its scenery is superb. (作主語)

3.I once ran into the same trouble as you did years ago. (作賓語)

另外，the same 之后也可以跟that 引導的定語從句表同一關系。

He has been admitted to the same university that his brother studies in.

二、在非限制性定語從句中

(一)as可用在句首或句中，而 which 引導的定語從句只用在句中。

1.As the world know， China successfully hosted the 29th Olympic Games in 2008.

2.The engineer was suddenly kidnapped， which surprised his college.

3.If Ken comes late， as is usual for another time， we will not receive him any more.

(二)which用作關系代詞，可用來代指上文某個詞也可以代指上文的整個句子，而 as只用來代指整個句子。

1.As was announced， only one of the participants passed the test.

2.The manager held a meeting， which lasted two hours.

(三)在which引導的定語從句中，謂語動詞若是am/is/are則這些系動詞不能省略;而若是as引導的定語從句，則系動詞可以省略。

1.The young girl is a teacher， as (is) clear from her manner. (is可省)

2.He said he had never seen her before， which was not true. (was不省)

(四)作主語時，which 既可以作系動詞be的主語也可以作實義動詞的主語;而as只作系動詞的主語。

1.He grows too fast， which makes him taller than his classmates.

2.Mother doesn’t like watching a comic opera， as/which is strange.

三、在下列情形中常用as不用 which

1.定語從句的謂語由實義動詞的被動形式構成

As is reported/announced/expected/said/well known/declared/can be seen/As may be imagined，…

As can be seen， the old man wouldn’t receive any offer.

2.As usually happened， …

As usually happened， the village was again struck by a fierce typhoon last summer.

3.感官動詞和意識類動詞作定語從句的謂語時。

see， hear， notice， know， learn， realize 等作謂語時，常用as 引導定語從句。

As you realize， he hates women smoking.

4.當定語從句有“如同……那樣”含義時，用as 比用which 更常見，而這些從句幾乎成為固定用法。

Things will turn out contrary to one’s wishes， as is often the case. 事與愿違，這是常有的事。