1. 用于引導(dǎo)限制性定語從句，主要與such, as, the same連用，其意為“像……的”“凡是……的”“……一類的人(物)”。如：
He’s not such a fool as he looks.
他并不像看上去的那樣愚蠢。
He is not such a man as would leave his work half done.
他并不是一個(gè)做事半途而廢的人。
You must show my wife the same respect as you show me.
你必須對(duì)我妻子表現(xiàn)出與對(duì)我同樣的敬重。
He smokes as expensive a cigarette as he can afford.
他抽一種他買得起的最貴的煙。
2. 用于引導(dǎo)非限制性定語從句，根據(jù)情況可位于主句之前或之后，有時(shí)也可插在主句中間，其意為“這件事”“這一點(diǎn)”。如(www.yygrammar.com)：
He is late, as is often the case.
他遲到了，這是經(jīng)常的事。
As is usual with children, they soon got tired.
孩子們一貫如此, 他們很快就厭倦了。
David, as you know, has not been well lately.
大衛(wèi)最近身體不太好，這你是知道的。
He’s not such a fool as he looks.
他并不像看上去的那樣愚蠢。
He is not such a man as would leave his work half done.
他并不是一個(gè)做事半途而廢的人。
You must show my wife the same respect as you show me.
你必須對(duì)我妻子表現(xiàn)出與對(duì)我同樣的敬重。
He smokes as expensive a cigarette as he can afford.
他抽一種他買得起的最貴的煙。
2. 用于引導(dǎo)非限制性定語從句，根據(jù)情況可位于主句之前或之后，有時(shí)也可插在主句中間，其意為“這件事”“這一點(diǎn)”。如(www.yygrammar.com)：
He is late, as is often the case.
他遲到了，這是經(jīng)常的事。
As is usual with children, they soon got tired.
孩子們一貫如此, 他們很快就厭倦了。
David, as you know, has not been well lately.
大衛(wèi)最近身體不太好，這你是知道的。