an, a是不定冠詞,僅用在單數(shù)可數(shù)名詞前面,表示“一”的意義,但不強調(diào)數(shù)目觀念.a用在以輔音（指輔音音素）開頭的詞前, an用在以元音（指元素音素）開頭的詞前,如：
a history class an island
a university an elephant
a hero an old man
不定冠詞的用法：
1. 表示人或事物的某一類
A plane is a machine that can fly.
2. 表示某一類人或事物中的任何一個.
This is an apple.
His father is a teacher.
3. 泛指某人或某物,但不具體說明何人何物.
A comrade is waiting for you downstairs.
I met an old man on my way to school.
4. 表示“一個”的意思
He will be back in a day or two.
He tried to send a picture of a face.
5. 有時也表示“每”的意思
We have three meals a day.
我們一日三餐.
He walks ten miles an hour.
他一小時走10英里.
We have six classes a day.
我們一天上六節(jié)課.
He drives the car at thirty miles an hour.
如果把不定冠詞后的名詞變?yōu)閺蛿?shù),只把不定冠詞去掉還不行,還得補上一個數(shù)詞或不定代詞（some, any）
The plan will be ready in a few days.
這是因為“一個”或“某個”變?yōu)閺蛿?shù)時,就成為“幾個”或“某幾個”的緣故.
定冠詞the具有確定的意思,用以特指人或事物,表示名詞所指的人或事物是同類中的特定的一個,以別于同類中其他的人或事物,相當于漢語中的“那個”或“這個”的意思.它可以和單、復數(shù)名詞,也可以和不可數(shù)的名詞連用.II定冠詞的基本用法：
1. 特指某（些）人或某（些）事物.
Give me the book.
Did you hear the talk given by Mr Li?
How do you like the film.
Have you got the letter?
2. 指談話雙方都知道的人或事物.
Where is the teacher?
Open the door.
3. 復述上文提過的人或事物.
I have a beautiful wallet, but the wallet was stolen yesterday.
4. 世界上獨一無二的事物等（月亮、地球、天空、宇宙）
The sun rises in the east.
The earth goes round the sun.
the globe, the universe.
the atmosphere大氣層
5. 用在方位名詞前
in the south, in the west ,in the north
6. 用在序數(shù)詞或形容詞最高級前
The first thing I want to say is to listen carefully in class.
He is the tallest one in our class.
7、表示兩者間“較……的一個”時用定冠詞
The older of the two noblemen took a light.
He is the taller of the two boys.
8. 用在單數(shù)可數(shù)可數(shù)名詞前表示一類人或事物.
The horse is a useful animal.
9. 定冠詞用在形容詞前,表示一類人或東西.
The rich, the poor ,the wounded ,the deaf