一、引导限制性定语从句

引导限制性定语从句时，在such, as, the same后只能用as，其他情况用 which。如：

I never heard such stories as he tells. 我从未听过他讲那样的故事。

It’s the same story as I heard yesterday. 这故事跟我昨天听到的一样。

Such wind as there was came up the fiver. 当时起的这种风沿江刮了上来。

He was in such a fury as I have never seen. 我从未见过他发这么大的火。

As many as ten people were found living in a single room. 曾发现多达十个人住在一间房里。

It is an organization which helps the elderly. 这是一个帮助老年人的机构。

He possesses qualities which ensure success at school. 他有许多品质保证他学习很成功。

 

二、引导非限制性定语从句

1. 互换的场合

引导非限制性定语从句时，有时两者可互换。如：

I live a long way from work, as [which] you know. 我住得离工作单位很远，这你是知道的。

He arrived early to dust the shop, as [which] was his custom. 他到车间很早，先掸尘土，这是他的习惯。

I had coffee after dinner, as [which] is my usual practice. 我饭后喝咖啡，这是我的习惯。

Sophia was not unconscious, as [which] could be judged from her eyes. 索菲娅并未失去知觉，这从她的眼睛里可以看出。

 

2. 不能互换的场合

在以下情况引导非限制性定语从句时，两者不可换用：

(1) 当从句位于主句之前时，只用 as。如：

As you know, next Tuesday’s meeting has been cancelled. 你知道，下周二的会议取消了。

As is known to everybody, the moon travels round the earth once every month. 月球每月绕地球转一周，这是每个人都清楚的。

 

(2) 当从句插在主句中间且关系代词指的是整个句子时，只用 as。如：

Freddie, as might be expected, was attending the conference. 弗雷迪在参加会议，这是可以预料到的。

 

(3) as 引导的非限制性定语从句应与主句在意义上和谐一致，which无此限制：

He went abroad, as [which] was expected. 他出国了，这是大家预料到的。

He went abroad, which was unexpected. 他出国了，这让大家感到很意外。(不用as)

 

(5) as 引导非限制性定语从句时，先行词通常不能是主句中某个具体的词，而应是整个句子、整个短语或某个短语推断出来的概念，而which 则无此限制：

Water, which is a clear liquid, has many uses. 水是一种清澈的液体，有许多用途。(不用as)

The river, which flows through London, is called the Thames. 这条流经伦敦的河叫泰晤士河。(不用as)

但是，若先行词不是某个具体的事物，而是一个抽象的概念，也可以用as。如：

The two brothers were satisfied with this decision, as was agreed beforehand. 两兄弟对此决定都满意，这项决定在事前已都得到他们的同意。

 

(6) 当as 引导非限制性定语从句作主语时，其谓语通常应是连系动词，而不宜是其他动词，而 which则无此限制：

She has married again, as [which] seemed natural. 她又结婚了，这似乎很自常。

She has married again, which delighted us. 她又结婚了，这使我们很高兴。(不用as)