引導語：關係代詞as引導定語從句時，既可以單獨使用，也可以與其它詞連用，其用法要比that和which更為複雜，值得注意。現將其歸納如下。
as引導定語從句與其它詞連用
A．用於the same．．．as．．．結構中
This is the same sickle as I lost yesterday．這把鐮刀和我昨天丟的那把一樣。
We drove out of the town by the same road as we had entered by．我們沿著進城的同一道路開車出城。
This is the same material as is used in building the bridge．這和建那座橋所用的材料一樣。注意：在這一結構中，as有時可以由that代替。例如：
I live in the same district as／that he lives in．我和他住在同一區。但兩者亦有區別：
1．當定語從句省略謂語部分時，要用as。例如：
She uses the same scent as you（do）／that you do．她用的香水和你的一樣。
This book of his is the same as yours．他的這本書和你的那本一樣。
2．在容易引起歧義時，慎用as和that。例如：
This is the same knife as I lost last week．（一般理解為：這把刀和我上週丟的那把相似。也可理解為：這是我上週丟的那把刀。）
This is the same knife that I lost last week．這是我上週丟的那把刀。
3．that在現代英語中可作關係副詞，而as則不可。例如：
I live in the same district that he lives．（不可用as。）
B．用於such．．．as．．．結構中
I never heard such stories as he tells．我從未聽過像他講的那種故事。
He was in such a fury as I've never seen．他怒氣之大，我從沒見過。
Such women as knew Tom thought he was charming．認識湯姆的`女人都認為他很有魅力。注：有時such和as連在一起用。例如：
We had hoped to give you a chance such as nobody else ever had．我們本希望給你一次別人不曾有過的機會。
We are living in a new era such as has never existed before．我們生活在前所未有的新時代。
C．用於“so＋adj．＋a（n）＋n．（單數）＋as結構中
We witnessed so great a parade as nobody ever dreamt of in preliberation days．我們見到在解放前沒有人曾經夢想過的一次盛大的。
I'm not so strong a man as I was．我已不像從前一樣健康了。
He's never written again so good a book as his first one．他再也沒寫出像他的第一部那麼好的書。
D．用於“as＋adj．＋n．＋as比較結構中
He is as learned a professor as works in the uni- versity．他是在這所大學工作的教授中最有學問的一個。
Some people have no doubt that their cat understands as many words as does a dog．許多人相信他們的貓跟狗懂的話一樣多。
They are as fine women as ever walked．她們可以與任何卓越的女性媲美。注：as．．．as．．．後面加上ever以加強語氣，表示“不亞於任何……”，“不弱於……”，有最高階的意味。又如：
He is as brave a man as ever lived．他是世界上最勇敢的人。二、as單獨引導定語從句
A．as單獨引導定語從句時，先行詞可以是一個詞，但更為常見的是：它的先行詞是整個主句，有時也可以是一個短語。例如：
The two brothers were satisfied with this decision，as was agreed to beforehand兩兄弟對此決定都很滿意，這項決定事前已得到他們的同意。（先行詞是decision）
She is late，as is often the case．她遲到了，這是經常的事。（先行詞是整個主句）
He married her，as was natural．他和她結婚了，這是很自然的。（先行詞是整個主句）
To shut your eyes to facts，as many of you do，is foolish．視而不見———你們好多人都是如此———是愚蠢的。
