冠词是虚词，本身不能单独使用，也没有词义，它用在名词的前面，帮助指明名词的含义。英语中的冠词有三种：定冠词、不定冠词、零冠词。

　　一、不定冠词的基本用法

　　不定冠词用于单数可数名词之前，其中 a 用于以辅音音素开始的词前。而 an 是用于以元音音素前等, 不是元音字母开始的词前。
如：a university，a useful tool，a computer，an orange，an hour，an 800-meter bridge
1、与可数名词单数连用，表示类别。 
例如：
--I knocked over my coffee cup. It went right over the keyboard.
--You shouldn't put drinks near a computer.
2、泛指某人或某物， 表示“某一个”，相当于 a certain。 
例如：
--Hello, could I speak to Mr. Smith?
--Sorry, wrong number. There isn't a Mr. Smith here.
3、用于数量、时间等名词前，表示“每一（单位）的……”相当于 per。 
例如：
I earn 10 dollars an hour as a supermarket cashier on Saturdays.
4、用于固定词组中。  
例如：a knowledge of ，have a gift for，give sb. a ride，a couple of，have a good time，keep a diary，in a hurry，once in a while，at a loss，tell a lie，do sb. a favor。

　　二、定冠词的基本用法

1、用来特指某（些）人或某（些）事物。所特指的名词常被短语或定语从句所修饰。
例如：
Of all the reasons for my decision to become a university professor, my father's advice was the most important one.
2、指说话的双方都知道的人或事物。 
例如：
Don't worry if you can't come to the party. I'll save some cake for you.
3、复述上文中提到的事物。
例如：
There is a shelf in my father's room. The shelf is new.
4、用于单数可数名词之前，表示该类事物，相当于 a。
例如：
When you come here for your holiday next time, don't go to the hotel; I can find you a bed in my flat.
5、序数词和形容词最高级前。比较级前若表示特指时也要用定冠词 the 。 
例如：
The cakes are delicious. He'd like to have a third one because the second one is rather too small.
I want to chat with the taller of the two men.
6、在表示方位、乐器的名词前。
例如：
Summer in the south of France is for the most part dry and sunny.
play the piano, play the violin