英语a/an的用法

a用在以辅音字母开头,或以读做辅音的元音字母开头的单词前面：
a man一个男人
a university一所大学
a hat一顶帽子
a European一个欧洲人
a one-way street一条单行马路
an用在以元音字母（a,e,i,o,u）开头,或以不发音的h字母开头的单词前面：
an apple一个苹果
an island一个岛
an uncle一位大叔
an onion一个洋葱
an egg一个鸡蛋
an hour一小时
an还用在发音以元音开头的单个字母前面：
an L－plate一块“实习驾驶”车牌
an MP一个国会*
an SOS一个呼救信号
an‘x’一个x字母、X形的东西或未知数
a／an没有性的变化：
a man一个男人
a woman一个女人
an actor一个男演员
an actress一个女演员
a table一张桌子
a／an不用在以下几种情况下：
A 复数名词之前：
a／an没有复数形式,所以a dog的复数是dogs,an egg的复数是eggs.
B 不可数名词之前（参见第13节）：
C 三餐名称之前,但这些名称前加形容词时除外：
We have breakfast at eight．
我们8点钟吃早饭.
He gave us a good breakfast．
他请我们吃了一顿丰盛的早餐.
为了庆祝某事或特意为某人而举行的宴会之前要用冠词：
I was invited to dinner（at their house, in the ordinary way）．
他们邀请我吃饭（在他们家吃便饭）.
但是说：
I was invited to a dinner given to welcome the new ambassador．
我被邀请参加欢迎新任大使的宴会.
A a／an和one（形容词）
1计算时间、测量距离或重量等时,a／an或one可以用于单数的前面：
￡l=a／one pound一英镑
￡ 1,000,000＝ a／one million pounds 100万英镑
（参见第三十六章.）
但是,请注意：
The rent is ￡ 100 a week．
房租为每星期100英镑.
这个句子中week前面的a不能用one代替.（参见第2节F.）
在其他类型的陈述句中a／an和one通常不能互换,因为one+名词通常意为 one only／not more than one（只有一个）,而a／an则没有这个意思：
A shotgun is no good．
猎枪不行.（这种武器不合适.）
One shotgun is no good．
一枝猎枪不行.（我需要两枝或三枝.）
2 one的特殊用法
（a） one（形容词／代词）与 another／others对照连用：
One（boy）wanted to read,another／others wanted to watch TV．一个（男孩）想看书,另一个／别的男孩们想看电视.（参见第53节.）
One day he wanted his lunch early, another day he wanted it late．
他一天要早点吃午饭,另一天又要晚点吃午饭.
（b） one可以用在 day／week／month／year／summer／winter等词之前,或者用在日期或月份的名称之前,以特指某事发生的时间：
One night there was a terrible storm．
一天晚上有一场特大的风暴.
One winter the snow fell early．
有一年冬天雪下得早.
On e day a telgram arrived．
有一天来了一封电报.
（c） one day也可用来表示 at some future date（将来有一天）：One day you’ll be sorry you treated him so badly．（这里也可用someday.）
终有一天你会因为待他这么不好而后悔的.
（关于one和you,参见第68节.）
B a／an和one（代词）
one是可以用来代替a／an的相应的代词形式：
-Did you get a ticket?
-Yes,I managed to get one．
-你搞到票了吗?
-是的,我设法搞到了一张.
具有这种用法的one的复数形式是some：
-Did you get tickets?
-Yes,I managed to get some．
-你搞到票了吗?
-是的,我设法搞了几张.
1.一(个,件,…)：
He had a book under his arm．他手臂下夹着一本书.
He was a boy from a poor home. 他是来自穷苦家庭的孩子.
I saw a girl watering the flowers. 我看见一个女孩在浇花.
Anna had a boy friend named James. 安娜有个男朋友名叫詹姆斯.
He arrived half an hour ago. 他是半小时前到达的.
He is an able man. 他是一个能干的人.
Give him an inch and he will take a mile. 他会得寸进尺.
The book is based on an actual case. 这书是根据一个实际案例写的.
He decided to put an advertisement in the newspapers. 他决定在报上登一份广告.
2.任何…都：
A bird has wings. 鸟有翅膀.
A square has four sides. 正方形有四条边.
A dog is an animal. 狗是动物.
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. 医生让他每天洗两次眼睛.
The ducks were force-fed several times a day. 这种鸭子每天强行喂食好几次.
4.某,某一个：
A Mr. Black just came to see you. 刚才一个叫布莱克先生的人来看你.
The house next door has been bought by a Mr Jones. 隔壁的房子被一个叫琼斯的先生的人买下了.
【考点说明】
1. 用 a 还是用an：一般说来,在辅音或半元音开头的词前用a,而在元音开头的词前用an.注意：有些以元音字母开头的单词,由于第一个音不是元音而是辅音,其前仍用a而不用an.
2. 单数可数名词若泛指,其前需加 a / an,不要从汉语习惯出发,漏掉此不定冠词,如不能说Her father is famous film poet.(应在is加a)
3.不能与指示代词、物主代词、名词所有格等连用,如不说 my a good friend,可改说 a good friend of mine.
不定冠词最基本的用途就是用来表示“一”这概念,如：
① A stitch in time saves nine.
② Jason is an internationally known scholar.
此外,a/an 还有下列 6 种用途：
一常和time、measurement等有关的名词连用,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 以及数目及数量连用,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”后面出现,以表示“同一类”这概念,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”等字后面出现,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 +形容词”这些结构里,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.
六出现在许多惯用语中,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