a用在以輔音字母開(kāi)頭,或以讀做輔音的元音字母開(kāi)頭的單詞前面：
a man一個(gè)男人
a university一所大學(xué)
a hat一頂帽子
a European一個(gè)歐洲人
a one-way street一條單行馬路
an用在以元音字母（a,e,i,o,u）開(kāi)頭,或以不發(fā)音的h字母開(kāi)頭的單詞前面：
an apple一個(gè)蘋果
an island一個(gè)島
an uncle一位大叔
an onion一個(gè)洋蔥
an egg一個(gè)雞蛋
an hour一小時(shí)
an還用在發(fā)音以元音開(kāi)頭的單個(gè)字母前面：
an L－plate一塊“實(shí)習(xí)駕駛”車牌
an MP一個(gè)國(guó)會(huì)議員
an SOS一個(gè)呼救信號(hào)
an‘x’一個(gè)x字母、X形的東西或未知數(shù)
a／an沒(méi)有性的變化：
a man一個(gè)男人
a woman一個(gè)女人
an actor一個(gè)男演員
an actress一個(gè)女演員
a table一張桌子
a／an不用在以下幾種情況下：
A 復(fù)數(shù)名詞之前：
a／an沒(méi)有復(fù)數(shù)形式,所以a dog的復(fù)數(shù)是dogs,an egg的復(fù)數(shù)是eggs.
B 不可數(shù)名詞之前（參見(jiàn)第13節(jié)）：
C 三餐名稱之前,但這些名稱前加形容詞時(shí)除外：
We have breakfast at eight．
我們8點(diǎn)鐘吃早飯.
He gave us a good breakfast．
他請(qǐng)我們吃了一頓豐盛的早餐.
為了慶祝某事或特意為某人而舉行的宴會(huì)之前要用冠詞：
I was invited to dinner（at their house, in the ordinary way）．
他們邀請(qǐng)我吃飯（在他們家吃便飯）.
但是說(shuō)：
I was invited to a dinner given to welcome the new ambassador．
我被邀請(qǐng)參加歡迎新任大使的宴會(huì).
A a／an和one（形容詞）
1計(jì)算時(shí)間、測(cè)量距離或重量等時(shí),a／an或one可以用于單數(shù)的前面：
￡l=a／one pound一英鎊
￡ 1,000,000＝ a／one million pounds 100萬(wàn)英鎊
（參見(jiàn)第三十六章.）
但是,請(qǐng)注意：
The rent is ￡ 100 a week．
房租為每星期100英鎊.
這個(gè)句子中week前面的a不能用one代替.（參見(jiàn)第2節(jié)F.）
在其他類型的陳述句中a／an和one通常不能互換,因?yàn)閛ne+名詞通常意為 one only／not more than one（只有一個(gè)）,而a／an則沒(méi)有這個(gè)意思：
A shotgun is no good．
獵槍不行.（這種武器不合適.）
One shotgun is no good．
一枝獵槍不行.（我需要兩枝或三枝.）
2 one的特殊用法
（a） one（形容詞／代詞）與 another／others對(duì)照連用：
One（boy）wanted to read,another／others wanted to watch TV．一個(gè)（男孩）想看書(shū),另一個(gè)／別的男孩們想看電視.（參見(jiàn)第53節(jié).）
One day he wanted his lunch early, another day he wanted it late．
他一天要早點(diǎn)吃午飯,另一天又要晚點(diǎn)吃午飯.
（b） one可以用在 day／week／month／year／summer／winter等詞之前,或者用在日期或月份的名稱之前,以特指某事發(fā)生的時(shí)間：
One night there was a terrible storm．
一天晚上有一場(chǎng)特大的風(fēng)暴.
One winter the snow fell early．
有一年冬天雪下得早.
On e day a telgram arrived．
有一天來(lái)了一封電報(bào).
（c） one day也可用來(lái)表示 at some future date（將來(lái)有一天）：One day you’ll be sorry you treated him so badly．（這里也可用someday.）
終有一天你會(huì)因?yàn)榇@么不好而后悔的.
（關(guān)于one和you,參見(jiàn)第68節(jié).）
B a／an和one（代詞）
one是可以用來(lái)代替a／an的相應(yīng)的代詞形式：
-Did you get a ticket?
-Yes,I managed to get one．
-你搞到票了嗎?
-是的,我設(shè)法搞到了一張.
具有這種用法的one的復(fù)數(shù)形式是some：
-Did you get tickets?
-Yes,I managed to get some．
-你搞到票了嗎?
-是的,我設(shè)法搞了幾張.
1.一(個(gè),件,…)：
He had a book under his arm．他手臂下夾著一本書(shū).
He was a boy from a poor home. 他是來(lái)自窮苦家庭的孩子.
I saw a girl watering the flowers. 我看見(jiàn)一個(gè)女孩在澆花.
Anna had a boy friend named James. 安娜有個(gè)男朋友名叫詹姆斯.
He arrived half an hour ago. 他是半小時(shí)前到達(dá)的.
He is an able man. 他是一個(gè)能干的人.
Give him an inch and he will take a mile. 他會(huì)得寸進(jìn)尺.
The book is based on an actual case. 這書(shū)是根據(jù)一個(gè)實(shí)際案例寫的.
He decided to put an advertisement in the newspapers. 他決定在報(bào)上登一份廣告.
2.任何…都：
A bird has wings. 鳥(niǎo)有翅膀.
A square has four sides. 正方形有四條邊.
A dog is an animal. 狗是動(dòng)物.
3.每(一)：
He comes home once a week. 他每周回一次家.
The doctor told him to bathe his eyes twice a day. 醫(yī)生讓他每天洗兩次眼睛.
The ducks were force-fed several times a day. 這種鴨子每天強(qiáng)行喂食好幾次.
4.某,某一個(gè)：
A Mr. Black just came to see you. 剛才一個(gè)叫布萊克先生的人來(lái)看你.
The house next door has been bought by a Mr Jones. 隔壁的房子被一個(gè)叫瓊斯的先生的人買下了.
【考點(diǎn)說(shuō)明】
1. 用 a 還是用an：一般說(shuō)來(lái),在輔音或半元音開(kāi)頭的詞前用a,而在元音開(kāi)頭的詞前用an.注意：有些以元音字母開(kāi)頭的單詞,由于第一個(gè)音不是元音而是輔音,其前仍用a而不用an.
2. 單數(shù)可數(shù)名詞若泛指,其前需加 a / an,不要從漢語(yǔ)習(xí)慣出發(fā),漏掉此不定冠詞,如不能說(shuō)Her father is famous film poet.(應(yīng)在is加a)
3.不能與指示代詞、物主代詞、名詞所有格等連用,如不說(shuō) my a good friend,可改說(shuō) a good friend of mine.
不定冠詞最基本的用途就是用來(lái)表示“一”這概念,如：
① A stitch in time saves nine.
② Jason is an internationally known scholar.
此外,a/an 還有下列 6 種用途：
一常和time、measurement等有關(guān)的名詞連用,以表示“每—” 的概念,如：
③ I teach five days a week.
④ This type of vegetables is sold at one dollar a kilo.
⑤ My car usually runs sixty kilometres an hour.
二常和 hundred, thousand, dozen 以及數(shù)目及數(shù)量連用,如：
⑥ That factory turns out at least a hundred tyres a day.
⑦ Noel's monthly salary is a thousand dollars.
⑧ I have a number of sponsored students.
⑨ Mary has a lot of money.
三在“of / at”后面出現(xiàn),以表示“同一類”這概念,如：
⑩ Birds of a feather flock together.
11. Please come one at a time.
12. Things of a kind come together, so do people of a mind.
四常在“rather, quite, many, half, what, such”等字后面出現(xiàn),形成固定用法,如：
13. Tom is rather a fool.
14. I think Chinese is quite a useful language.
15. Many a student has asked that question.
16. The visitor left half an hour ago.
17. What a fine day it is!
18. How can you say such a thing?
五用在“so, as, too, how +形容詞”這些結(jié)構(gòu)里,如：
19. We have not had so hot a day before.
20. Susan is as clever a girl as Anna.
21. That is too difficult a book for beginners.
22. No one knew how serious a problem it was until later.
六出現(xiàn)在許多慣用語(yǔ)中,如：
23. Bob always has a bone to pick with others.
24. Some students turned a deaf ear to the teacher's advice.
25. All must learn a language with an eye to mastering it.
26. I hope you will make an effort to attend the meeting punctually.
27. Jason has an aversion to being idle.
28. The news of Jack's sudden resignation came as a bolt from the blue