关系代词which和as的区别

 　　我们都知道，which和as都可以引导非限制性定语从句，有时可以互换使用。但两者的用法又有所不同。何时用which，何时又必须用as?是不是有些傻傻分不清?!来来来，今天就把这个问题一次拎清~~~

　　(1)位置上，as可放在句首、句末，也可插入主句中;which一般放在主句之后(有时也可用as)：

　　As we all know, reading is very important.

　　Reading is very important, which we have already known¹ when we were very young.

　　(2)意义上，as有正如、按照、正像之意，一般用在肯定句中;which可用于含肯、否定意义的句子中：

　　He failed in the exam again, as was expected.

　　He failed in the exam again, which was unexpected².

　　(3)当定语从句所修饰的主句内容是谓语动词的对象时，常用as，如：

　　Jack³ was admitted into the university, as we had expected.

　　(4)固定结构，用as：

　　as has been said before as often happens

　　as is well known as we all can see

　　the same...as such...as

　　(5)当关系代词代表主句引起的结果，又做主谓宾补(SVOC)结构中的主语时，多用which：

　　He passed the exam, which made him delighted.

　　(6)在从句中作介词宾语时，用which，如：

　　They went to the zoo, after which they saw a film.

　　(7)在从句中代表主句中的谓语的整个概念时，常用which，如：

　　He can write a letter in English, which I cannot.

　　(8)指代主句中某一名词时，多用which，如：

　　Beijing, which he was born, is our capital.

　　(9)代替主句中的形容词时, 常用which，如：

　　Lily thought me clever, which she herself was.

　　在定语从句中，相比于which VS that，who VS that，我们对which与as两者区别的关注度要少很多，在遣词造句或是口语表达中，也常常是“跟着感觉走”。

1 known   

adj.大家知道的；知名的，已知的

参考例句：

• He is a known artist.他是一个知名的艺术家。
• He is known both as a painter and as a statesman.他是知名的画家及政治家。

2 unexpected   

adj.想不到的，意外的

参考例句：

• I always keep some good wine in for unexpected guests.我总保存些好酒，用来招待不速之客。
• His promotion was unexpected.他的升迁出人意料。

3 jack   

n.插座，千斤顶，男人；v.抬起，提醒，扛举；n.（Jake）杰克

参考例句：

• I am looking for the headphone jack.我正在找寻头戴式耳机插孔。
• He lifted the car with a jack to change the flat tyre.他用千斤顶把车顶起来换下瘪轮胎。