一、作副词，意为“相同地”，“同样地”。例如：
They don’t have as many airplanes. 他们没有同样多的飞机。
二、作连词，
1. 引导时间状语从句
as与when，while都是引导时间状语从句的从属连词，含义都是"当……的时候"。但它们有区别:
1). when作“当……的时候”解，可以指较短的(一点)时间,也可指一段时间。从句的动作可以与主句的动作同时发生，也可以先于主句的动作发生。例如:
John was having his dinner when I saw him. 当我看到约翰的时候，他正在吃饭。
She can write only when the baby is asleep. 只有婴儿睡着的时候，她才能写作。
2). 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或在从句动作过程中发生。例如:
We must strike while the iron is hot. 要趁热打铁。
While we were reading, the teacher came in. 我们正在读书的时候，老师走了进来。
3). 但属下列情形时，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……”。例如:
The girl dances as she sings on the stage.那个女孩在舞台边唱歌边跳舞。
He looked behind from time to time as he went forward. 当他朝前走时，不时地向后看。
② 表示两个同步发展的动作或行为,译为“随着……”。例如:
As time went on / by, she became more and more worried. 随着时间的流逝，她变得越来越焦虑。
As he grew older, he became more intelligent. 随着他年龄的增长，他变得更有才智了。
③ 表示两个短促行为或事件几乎同时发生。例如:
I thought of it just as you opened your mouth. 恰好在你开口时，我想到了它。
Just as the flying worm hit her face, she gave a loud cry. 恰巧在飞虫撞到她脸上时，她大哭起来。
2. 引导原因状语从句
as，because，since都可以表示因果关系，连接原因状语从句，含义是“因为，由于”，但它们有区别：because表示的语气最强;as一般放在句首，语气较弱，较口语化;since常常用在书面语中，表示多为对方已知的、或稍加分析便可得知的原因，有时可译作“既然”。例如：
I do it because I like it. 我做这件事是因为我喜欢。
Since many of the customers work during the day, Billy has to collect the money at night. 因为许多顾客白天上班,所以毕利只好晚上去收钱。
As she has been ill perhaps she'll need some help. 她由于生病可能需要些帮助。
3. 引导让步状语从句
as与although (或though)，however (或no matter how)等都可以引导让步状语从句，含义是“虽然，尽管”，但它们有区别：although语气稍正式些，可放在句首，也可放在句中，主句中不能再用 but，但可以用yet;as所表示的语气较强，引导的让步状语从句用倒装语序;however引导让步状语从句时，它的后面可跟形容词或副词，也要用倒装语序。例如：
Although they are poor they are happy. 虽然他们很穷，但很快乐。
Angry as he was, he managed to speak calmly. 虽然他很生气，但是他讲话很平静。
However hard the question is, he can answer it. 不管问题有多难他都能回答。
注意：当as引导让步状语从句时，句子的倒装语序有以下三种形式：
1). 形容词或副词+as+主语+连系动词be或实义动词。例如：
Rich as he is, he never spends a cent on clothes. 虽然他很富有，但他从不花一分钱在衣服上。
Much as I admire his courage, I don’t think he acted wisely. 我虽然佩服他的勇气，但我认为他这样做是不聪明的。
2). 名词+as+主语+连系动词be (注意句首的名词不带冠词)。例如：
Child as he is, he knows a lot. 尽管他是个孩子，但懂很多事情。
Boy as he was, he was chosen king. 尽管他还是个孩子，但却被立为国王。
3). 实义动词+as+主语+助动词[如果没有助动词，则要加上一个do(does或did)]。例如：
Try as he may, he never succeeds. 尽管他很努力，但总是不成功。
Change your mind as you will, you will gain no additional support. 即使你改变主意，你也不会得到另外的支持。
4. 引导方式状语从句，意为“如”，“像”，“按照……的方式”。如:
I want you to tell my friend your very interesting experience exactly as you have told it to me. 我想让你像给我讲述的那样，给我的朋友讲一讲你那段极其有趣的经历。
Remember, you must do everything as I do. 记住，你必须按照我做的那样做一切。
注意：like在非正式语体中可以有与as相同的用法。如：
I can’t sing like I used to.我不能像以前那样唱歌了。
He writes just like his brother did when he was young. 他现在写文章正像他哥哥年轻时写文章一样。
5. 引导比较状语从句,用于“as...as...或 not so/ as...as...”中,前一个as是副词,后一个as是连词，意为“如(不如)…一样”。如:
1). You hate her as much as I (=as I hate her).
2). I don't speak English so/ as well as he does.
注意：句中连词as后面的代词实际是省略了与主句相同的部分，即例(1)可以写成You hate her as much as I hate her. 如果很明显就能看出所省略的部分，意义不会含糊不清时，在口语中也可以用代词的宾格形式。例：At your age you can’t expect to play football as well as me (= as I do).但例(1)就不能改I为me，改后意思就变为：You hate her as much as you hate me. 你恨她像恨我一样深;而原句的意思为：你恨她像我恨她一样深。
三、作代词
as作关系代词的用法
关系代词as引导定语从句时，既可以单独使用，也可以与其他词连用，其用法要比that和 which更为复杂。
1. as引导定语从句与其他词连用
1). 用于the same...as结构中
This is the same watch as I have lost. 这块手表跟我丢失的那块一样。
2). 用于such...as结构中
I don’t like such novels as you recommend. 我不喜欢你推荐的那些小说。
3). 用于"so +adj. + a/an + n. (单数) + as "结构中
I am not so strong a man as I was. 我已经没有从前那么强壮了。
2. as单独引导定语从句
as单独引导定语从句时，先行词可以是一个词，也可以是一个句子或短语。例如：
1) She is late, as is often the case. 她迟到了，这是经常的事。(先行词是整个主句)
2) To shut your eyes to facts, as many of you do, is foolish. 对事实视而不见--你们好多人都是如此的愚蠢。(先行词是不定式短语)
注意1：(1). 当as引导的定语从句位于具有否定意义的主句之前时，as从句所修饰的范围是整个主句的内容，也就是说，把否定意义也包括在内。例如：
As has been said above, grammar is not a set of dead rules. 正如前面所说，语法不是一套死条文。
2). 当as引导的定语从句位于具有否定意义的主句之后时，as从句所修饰的范围不包括否定意义。例如：
Spiders are not insects, as many people think. = Spiders are not insects. But many people think they are. 许多人认为蜘蛛是昆虫，但蜘蛛并不是昆虫。
3). 当as引导的定语从句位于具有否定意义的主句中间时，as从句所修饰的范围也不包括否定意义。例如：
She did not, as her friend had feared, open the case. 她没有打开盒子，而她的朋友就是怕她当面打开盒子。
注意2: 当修饰句子的非限制性定语从句位于句尾时，as可以用which来替代。例如：
I live a long way from work, as (which) you know. 我住得离工作单位很远，这你是知道的。
但是，当as从句位于句首或句中是，as就不能用which来替代了。例如：
As you will find out, I will never let you down. 你将会发现，我绝不会使你失望的。
Taiwan is, as you know, an inseparable part of China. 你们知道，台湾是中国不可分割的一部分。
此外，如果主句为否定句，则位于句末和句中的as从句所修饰的范围并不包括主句的否定意义，此时，as也不能用while来替代。例如：
Greenland was not a continent, as people thought. 格陵兰并不像人们所想象的那样是一个大陆。
四、作介词，
1. 表示 “好像(某人)”，例如:
They entered the building disguised as cleaners. 他们化装成清洁工人的模样进入大楼。
2. 表示“作为，当作”，例如：
I found a job as a teacher. 我找了一份教师的工作。
3. 表示“当某人是(某身份)时。例如：
As a child, she was sent to three different countries. 她儿时去过三个不同的国家。
4. 表示“因某人是(某身份)”，例如：
As her private secretary he has access to all her correspondence. 他是她的私人秘书，能接触到她所有的信件。
注意1：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。例如:
As a Party member, I'll take the lead in everything. (状语)
She works as a nurse. (状语)
Tom has me as one of his best friends. (引起宾语补足语)
注意2：as和like都可以作介词，但意义不同。as表示“以实际的身份或地位”。 like则表示“与…相似，以与…相类似的方式”。例如：
1). He spoke as a teacher.
2). He spoke like a teacher.
句(1)的意思是：“他作为老师发言”或“他以老师的身份发言”。句(2)的意思是：“他讲话很像是老师”。
五、用于一些固定搭配
1. as good as差不多，几乎
Don’t worry, the matter’s as good as settled. 别担心，问题差不多已经解决了。
When the car was repaired, it looked as good as new. 这辆汽车修理好的时候，看起来差不多就像新的一样。
2. as if /as though 似乎;好像
He behaved as if nothing had happened. 他装着若无其事的样子。
She treats him as though he was her own son. 她待他好像待自己的儿子一样。
另外，as if可以接一个动词不定式短语。例如：
He waved his hand to me as if to have something to tell me. 他向我挥手好像有什么要告诉我。
3. as well as 同(一样也);和;还
Joan can speak Chinese as well as English. 琼能讲英语还能讲汉语。
He spent all his money, as well as wasting his time. 他不仅浪费了时间，还花光了他所有的钱。
4. such...as, such as 像……这样的
I bought a lot of fruits, such as apples, oranges, bananas and so on. 我买了许多种水果，像苹果，桔子，香蕉等。
We had such books as you never saw. 我们有一些你从未看过的书。
5. as for 至于某人(某事物)
We had a delightful weekend in the country. As for the traffic, we had no difficulty. 在乡下我们度过了一个愉快的周末。至于交通，我们没遇到任何困难。
6. as to 关于某事物;提到某事物
I don't know anything as to the others. 至于其他，我一无所知。
7. so as to ... 以便, 为了
Students should take notes so as to make revision easier. 学生应当记笔记，以便容易复习。
8. as a matter of fact 其实;实际上
As a matter of fact, I’m very fond of housework. 其实，我很喜欢做家务。
9. as a result 结果 (发生某种情况)
As a result， he had been given an excellent job. 结果，他得到了一份极好的工作。
10. as long as 只要
You may borrow this book as long as you promise to give it back. 只要你答应归还，你就可以把这书借走。
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，应付自如。
巩固练习
1. She had a tense expression on her face, ________she were expecting trouble.
A. even though B. even as C. as though D. now that
2. A good many proposals were raised by the delegates, ________was to be expected.
A. that B. what C. so D. as
3. ________might be expected, the response to the question was very mixed.A. As B. That C. It D. What
4. Americans eat ________as they actually need every day.
A. twice as much protein B. twice protein as much
C. twice protein as much D. protein as twice much
5. The trumpet player was certainly loud. But I wasn't bothered by his loudness ________by his lack of talent.
A. than B. more than C. as D. so much as
6. Studies show that the things that contribute most to a sense of happiness cannot be bought, ________a good family life, friendship and work satisfaction.
A. as for B. in view of C. in case of D. such as
7. ________he works hard, I don't mind when he finishes the experiment.A. As soon as B. So far as C. As well as D. As long as
8. ________the danger from enemy action, people had to cope with a severe shortage of food, clothing, fuel and almost everything.
A. As long as B. As far as C. As soon as D. As well as
Key: 1-5 CDAAD 6-8 DDD
A. an art much as B. much an art as
C. as an art much as D. as much an art as
2. She doesn't speak ______her friend, but her written work is excellent.
A. as well as B. so often as C. so much as D. as good as
3. The piano in the other shop will be ______, but ______.
A. cheaper; not as better B. more cheap; not as better
C. cheaper; not as good D. more cheap; not as good
4. After supper she would sit down by the fire, sometimes for ______an hour, thinking of her young and happy days.
A. as long as B. as soon as C. as much as D. as many as
5. With the help of the German experts, the factory produced ______ cars in 1993 as the year before.
A. as twice many B. as many as twice
C. as twice as many D. twice as many
6. After the new technique was introduced, the factory produced______ tractors in 1988 as the year before.
A. as twice many B. as many twice C. twice as many D. twice many as
7. ______, he doesn't study well.
A. As he is clever B. He is as clever C. Clever as he is D. As clever he is
8. ______, he was unable to make much progress.
A. Hard as he try B. Hard as he tried
C. As he tried hard D. He tried hard
9. Tom kept quiet about the accident ________ lose his job.
A. so not as to B. so as not to C. so as to not D. not so as to
10. When a pencil is partly in a glass of water, it looks as if it ______.
A. breaks B. has broken C. were broken D. had been broken
11. ________ is known to everybody, the moon travels round the earth once every month.
A. It B. As C. That D. What
12. ________ is known to all, China will be an ________ and powerful country in 20 or 30 years' time.
A. That; advancing B. This; advanced C. As; advanced D. It; advancing
13. He doesn't believe ________things ________ you do.
A. the same; as B. the same; with C. as same; as D. as same; with
14. ________ is mentioned above, the number of the students in senior high schools is increasing.
A. Which B. As C. That D. It
Key: 1-5 DACAD 6-10 CCBBC 11-14 BCAB