Same noun used with all three articles conveys different meaning:
  • He is at a school. (We don’t know which school.)
  • He is at the school. (We know which school.)
  • He is at school. (He is a teacher or student and is teaching or learning.)
  • I buy the paper every day. (Newspaper)
  • The professor presented a paper on recent findings about cancer cells. (A piece of writing)
  • The children are learning the art of folding paper into decorative objects. (Material)

 

It helps to observe the following:

1. When we use two or more adjectives to describe the same person or thing, we use the article only before the first adjective.

  • He talked to a tall and blonde woman. (He talked to a (one) woman who was tall and blonde.)

2. When we use two or more adjectives to refer to more than one person or thing, we use the article before each adjective.

  • He talked to a tall and a blonde woman. (He talked to two women, one of whom was tall and the other was a blonde.)