as可以作連詞、介詞及關系代詞。現將其用法小結如下:

一、 as作連詞的用法:

1. 作"當……的時候",引導時間狀語從句。注意與when、 while的用法區別。

① when作"當……的時候"解,可以指較短的(一點)時間,也可指一段時間。如:

When he was at college, he could speak several foreign languages.

When the clock struck twelve, all the lights in the street went out.

② while常表示一段較長的時間或一個過程,強調主句謂語動詞與從句謂語動詞同時發生。如:

Work while you work. Play while you play.

③ 但屬下列情形時,只用as, 而不用when或while。

A) 用于表示同一個人的兩種動作交替進行,指"一邊……,一邊……"。如:

The girl dances as she sings on the stage.

He looked behind from time to time as he went forward.

B)表示兩個同步發展的動作或行為,譯為"隨著……"。如:

As time went on / by, she became more and more worried.

As children get older, they become more and more interested in the things around them.

C)表示兩個短促行為或事件幾乎同時發生。如:

I thought of it just as you opened your mouth.

Just as the flying worm hit her face, she gave a loud cry.

D) 后接名詞表示某一年齡段時,用as。如:

As a young man, he was active in sports.

2. as=since, 作"既然"、"由于"解,引導原因狀語從句,常用來表示已為人們所知或顯而易見的原因或理由。如:

As / Since you’’’’re not feeling well, you may stay at home.

As he wasn’’’’t ready in time, we went without him.

3. as=in the way that, 作"像"、"按照……的方式"解,引導方式狀語從句。如:

He speaks English as Americans do.

Remember, you must do everything as I do.

4. 用于as...as...或not so/ as...as...中,前一個as是副詞,后一個as是連詞,引導比較狀語從句。如:

They helped the old man as often as possible.

I don’’’’t speak English so/ as well as he does.

5. 作"雖然"、"盡管"解,引導讓步狀語從句。常用倒裝語序,即adj. /adv. / n.+as +主語+謂語+主句。如:

Tired as they were, they walked on.

Child as he is, he knows a lot. (child前不用冠詞)

二、 as作關系代詞,引導定語從句,作"正如"、"這一點"解。如:

He is very careful, as his work shows.

As is well-known, Taiwan belongs to China.

as的這種用法,請看2001年的高考題:

is known to everybody, the moon travels round the earth once every month.

A. It B. As C. That D. What

(字母下劃橫線的為正確答案)

另外,當先行詞被the same, such等詞修飾時,常用as來引導定語從句。如:

Such a clever boy as he can learn anything quickly.

I was reading the same book as he bought yesterday.

三、 as作介詞的用法:

as引導的介詞短語大多用作狀語,as譯為"作為";少數情況可引起賓語補足語。如:

As a League member, I’’’’ll take the lead in everything. (狀語)

She works as a doctor. (狀語)

They have me as one of their own children.(引起賓語補足語)