as可用作连词,引导比较、时间、原因及方式等四种状语从句,应注意的是,引导的比较状语从句往往有省略;引导的时间状语从句一般用一般现在时而不用一般将来时;引导原因状语从句时与“Because”和“since”引导的从句比较起起来语气最弱.

as作介词,意思时“作为”,“以……身份”.例如：He came to China as a tourist five years ago.

而表示像…一样时,like通常作介词用,而介词后面通常接名词,代名词和动名词.

现将其用法小结如下:

(一)、 as作连词的用法:

1.作“在-------期间,当----的时候”引导时间状语从句.注意与when、 while的用法区别.

①下列情形时,只用as,而不用when或while.

1)用于表示同一个人的两种动作交替进行,指一边----一边.如:

The girl sings as she goes to school.

He looked behind occasionally as he went forward in the forest.

2)表示两个同步发生的动作或行?意思是随着-----的发展.如:

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

As children get older,they become more and more interested in everything.

3)表示两个短暂行为或事情几乎同时发生.如:I watched her as she read the book.

I thought of it just as you opened your mouth.

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

4)接在名词后面表示某一个年龄段时.如:

As a young man,he was active in sports.

②when作"当……的时候"解,可以指较短的(一点)时间,也可指一段时间.如:When I was at college,I could speak several foreign languages.When the clock struck twelve,I had slept for 2hours.

③ while常表示一段较长的时间或一个过程,强调主句谓语动词与从句谓语动词同时发生.如:Work while you work.Play while you play.

2.As =Since 作"既然"、"由于"解,引导原因状语从句,常用来表示已为人们所知或显而易见的原因或理由.如:As he’s been ill for ages,I will help him.

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

As he wasn't ready ,we went without him.

3.As =in the way that作"像"、"按照……的方式"解,引导方式状语从句.如:

Do as I told you.

Remember,you must do everything as I do.

4.用于as--- as或not / so/ as ---- as中,前一个as是副词,后一个as是连词,引导比较状语从句.如:They helped the old as much as possible.

I don't speak English so/ as well as she does.

5.表示虽然,尽管 等,引导让步状语从句,常用倒装语序,模式为:

adj./adv./ n.+as +主语+谓语+主句.如:Young as he is,he knows much.

Tired as they were,they walked on.

6.表示也------一样.She is a doctor,as was her husband.

(二)、 as作关系代词,引导定语从句,表示正如,这一点.如:

He is very careful,as we all know.

As is well-known,Taiwan belongs to China.

另外,当先行词被the same,such等词修饰时,常用as来引导定语从句.如:

Such a clever girl as she can learn anything quickly.

I was reading the same book as he bought yesterday.

(三)、as作介词的用法.

1.表示好像.如:He dressed as a policeman.

2.表示作为当作.如：I found a job as a guide.

3.当某人是某身份时.如：As a child ,she was sent to abroad.

4.as引导的介词短语大多用作状语,as译为"作为";少数情况可引起宾语补足语.如:

As a Party member,I'll take the lead in everything.(状语)

She works as a model.(状语)

She has me as one of her best friends.(引起宾语补足语)

(四)、作副词的用法 1 表示与------等同.如：This dress is twice as expensive as that one.2 像,如等.如：As before,he remained unmoved.

总之,通过以上的分析,我们对as的词性和用法有了比较全面的理解和把握,才能在实际的运用中做到心中有数,应付裕如.