(1)特指某(些)人或某(些)物： The ruler is on the desk.

(2)复述上文提到的人或物：He has a sweater. The sweater is new.

(3)谈话双方都知道的人或物：The boys aren’t at school.

(4)在序数词前： John’s birthday is February the second.

(5)用于固定词组中： in the morning / afternoon / evening

不用冠词的情况：

(1)专有名词前：China is a big country.

(2)名词前有定语：this , that , my , your , some, any , no 等：

This is my baseball.

(3)复数名词表示一类人和事：Monkeys can’t swim. They are teachers.

(4)在节日，日期，月份，季节前：Today is Christmas Day. It’s Sunday.

   (5)一日三餐前：We have breakfast at 6:30.