A/An vs. The (In English Language)

• A/An vs. The 

• 
• There are three articles in English: 

  -a

  -an

  -the

  
  

  -Use a/an with general nouns. 

  General nouns are not specific, they are any person/place/thing.

  A customer in the restaurant gave me a tip.

  I'd like a glass of water.

  
  

  -Use the with specific nouns. 

  Specific nouns are a person/place/thing you already know.

  The children in the playground are eating cupcakes.

  I saw the President on TV.
• -Use the to introduce a person/place/thing for the second time or name a specific person/place/thing.

  I am reading a book. The book is about the history of computers.
• a book = general 
  

  the book = second use of "book"
  

  the history of computers = specific 

 

Source : Alison