1. Indefinite article (不定冠词)
我们用 "a ， an " 当我们不知道他是诸多人或事中的哪一个：
* is one of many. ( 是许多个中的一个)
He is an artist.(=there are many artists)
* is not unique. (不是唯一的)
I have just bought a book
* has not been mentioned before. (之前没有提到过)
There was a new student in class today.
2. Definite article (定冠词)
我们用 " the " 当我们知道他是诸多人或事中的哪一个：
* is unique (or unique in that context) (是唯一的)
The Australian Prime Minister. (=there is only one)
I looked inside， the engine was in a terrible state.(=there is only one engine， in this case)
* has been mentioned before. (之前提到过)
The man gave me a ticket. I looked at it， and saw thatthe ticket was a single.
* is defined by the phrase which follows it. (要被接下来的短语详细说明)
What is the new student's name?
3. No articles (无冠词)
* using plural or uncountable nouns (在使用复数或不可数名词时)
Do you like sport?
* with the names of people or places， but there aremany exceptions (人名和地名的时候不用冠词，但是地名有许多例外)
He is Professor Jones
4. Fixed phrases ( 固定短语)