(一)、 as作連詞的用法:
as作連詞，常用來連接主句和狀語從句。
1.引導時間狀語從句，作“當...的時候”解，有“隨着...”之意，與while意義相近，強調兩個動作同時發生;或某事一發生，另一事立即發生。eg：
He shouted aloud as her ran along.他一邊往前跑，一邊高聲地呼喊。
I was startled as he opened the door.他一開門，我嚇了一跳。
as作連詞，相當於when。eg;
As a little boy (When he was a little boy)he began to learn to play piano.他小時候就開始學彈鋼琴。
2.引導原因狀語從句，作“因爲，由於”解，與because的用法相近。eg;
I must stop writing now，as I have rather a lot of work to do.我必須停筆了，因爲我還有許多工作要做。
3.引導方式狀語從句或比較狀語從句，作“正如，(如)像”解。例eg：
As in your country，we grow wheat in the north and rice in the south.正如(像)你們國家一樣，我們在北方種小麥，在南方種大米。(方式狀語從句)
When at Rome，do as Romans do.入鄉隨俗。(方式狀語從句)
4.引導讓步狀語從句，作“雖然，儘管”解。這時從句常用倒裝語序，即把從句中的表語、狀語或動詞原形放在as之前。eg;
Strange as it may seem，it is true.儘管這事看上去很奇怪，但卻是真的。
Try as he might，Tom could not get out of the difficulties.不管怎樣努力，湯姆還是擺脫不了困境。
1. 作“在-------期間，當----的時候”引導時間狀語從句.注意與 when、 while的用法區別。
時間狀語從句：as的用法
1.某事一發生，另一事立即發生
As the sun rose the frog dispersed 太陽一出來霧就消散。
They strolled into the garden as the music ceased. 音樂聲一停，他們就走進花園。
2.在某事發生的過程中另一事發生
I heard the murmur of their voices as I crossed the hall.
我走過大廳的時候聽到他們在嘀咕什麼。(兩個動作都是一般時態)
Just as he was speaking there was a loud explosion.
正當他在說話的時候，一聲巨響。(從句用進行時態)
3. 兩個動作同時發生
He smiled as he passed. 他路過的時候笑了一下。
As she sang, the tears ran down her cheeks. 她一邊唱歌，眼淚一邊從臉頰淌下。
Helen heard the story as she washed. 海倫一邊洗衣服一邊聽故事。
He saw that she was smiling as she read. 他看到她一邊看着書一邊笑。
(兩個都是延續性動作)
We get wiser as we get older. 我們隨着年齡的增長而變得聰明起來。
(隨着時間的變化而變化)
①下列情形時,只用as, 而不用when或while。
1) 用於表示同一個人的兩種動作交替進行,指一邊----一邊. 如:
The girl sings as she goes to school.
He looked behind occasionally as he went forward in the forest.
2)表示兩個同步發生的動作或行爲,意思是隨着-----的發展.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)表示兩個短暫行爲或事情幾乎同時發生.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)接在名詞後面表示某一個年齡段時.如:
As a young man, he was active in sports.
②when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 I was at college, I could speak several foreign languages. When the clock struck twelve, I had slept for 2hours.
③while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.
2. As =Since 作"既然"、"由於"解,引導原因狀語從句,常用來表示已爲人們所知或顯而易見的原因或理由。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.
=in the way that作"像"、"按照……的方式"解,引導方式狀語從句。如:
Do as I told you.
Remember, you must do everything as I do.
4. 用於as--- as或not / so/ as ---- as中, 前一個as是副詞, 後一個as是連詞, 引導比較狀語從句。如:
They helped the old as much as possible.
I don't speak English so/ as well as she does.
5. 表示雖然, 儘管 等, 引導讓步狀語從句, 常用倒裝語序, 模式爲:
adj. /adv. / n.+as +主語+謂語+主句。如:
Young as he is, he knows much.
Tired as they were, they walked on.
6. 表示也------一樣。
S he is a doctor, as was her husband.
(二)、 as作關係代詞,引導定語從句,表示正如,這一點.如:
1. 引導限制性定語從句，用在“”, “the ”，“”等結構中，常譯作“像...一樣的人(或物)”，“凡是...的人(或物)”。
eg： He wished to be such a man as Lei Feng was.他曾希望做一個像雷鋒那樣的人。
My hometown is no longer the same as it was.我的家鄉再也不像過去一樣了。
2.引導非限制性定語從句，用來指代它前面的整個句子(即先行句)，意思是“這一點”。這個分句可以位於句首、句中或句末。
eg：As is well known，oceans cover more than 70% of the earth.
我們知道，海洋佔地球面積的百分之七十以上。
He is very careful, as we all know.
As is well-known, belongs to China.
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 girl as she can learn anything quickly.
I was reading the same book as he bought yesterday.
(三)、as作介詞的用法.
1. 作“如，像”解,表示好像。如:He dressed as a policeman.
They got united as one man.他們團結得像一個人一樣。
2. 作“充當，作爲”解,表示作爲, 當作。如：I found a job as a guide.
As a writer，he was famous.作爲作家，他是很有名的。
3.當某人是某身份時。如：As a child , she was sent to abroad.
引導的介詞短語大多用作狀語,as譯爲"作爲";少數情況可引起賓語補足語。如:
As a Party member, I'll take the lead in everything. (狀語)
She works as a model. (狀語)
She has me as one of her best friends.(引起賓語補足語)
(四)、作副詞的用法
as作副詞，表示程度，意爲“同樣地”。在“...”，“not ...”結構中的`第一個as是副詞，作“和/與...(不)一樣”解。
e.g. Jack is as tall as his father.傑克和他的父親一樣高。
He doesn't speak English as/so fluently as you.他的英語說得不如你流利
1 表示與------等同。
如：This dress is twice as expensive as that one.
2 像，如等。
如：As before, he remained unmoved.
五)含as的固定詞組的用法
1. as soon as作“一…就”解，引導時間狀語從句。
eg：As soon as I get to Beijing，I'll write to you.我一到北京，就給你寫信。
long as作“只要”解，
e.g. As/So long as you study hard，you'll make progress.只要你努力，你就會取得進步。
2. as if/though常用來引導方式狀語從句，作“好像，彷彿”解。如果從句中講的是非真實情況，則用虛擬語氣。
e.g. She loves the child as if/though he were her own.
她愛這個孩子如同愛自己的孩子。
3. As if/though也可用來引導表語從句，常用在“It appears/looks/seems...+as if/though”句型結構中。
e.g. It appears as if/though it is going to clear up.看起來天要晴了。
It seems as if/though he knew nothing about it.他好像對此事一無所知。 to作“關於，至於”解。
e.g. There is no doubt as to his honesty.他的誠實是無可置疑的。
much/many as作“多達...”，“達到...之多”解。
e.g：He can earn as much as 5000 dollars a month.他每月能掙5000美元。
far as I know作“就我所知”解，在句中作插入語。
eg： As/So far as I know，he will come here next Monday.
據我所知，他將於下星期一到這裏來。
a result，as a result of表示“由於...的結果”。
e.g. She died as a direct result of the accident.她的死是那次事故的直接結果。
8，as well爲“也，還”之意。
e.g. Come early，and bring your brother as well.早點來，把你的弟弟也帶來。
as to， to若跟動詞原形，表示目的或結果。
eg：He studied hard so as to pass the exam.他努力學習以便通過考試。(表示目的)
