When do we use articles a and an?

• To refer to a person or a thing that you're mentioning for the first time. E.g. A man was seen driving a car.

• To refer to a person or a thing you don't want to be specific about. E.g. I went to eat to a restaurant yesterday.

• To refer to a person's profession. E.g. My father is a bus driver.

• To give definitions. E.g. An octopus is a sea creature with eight tentacles.

When do we use the definite article "the"?

• Used to refer to things the speakers already know about. The things they know of is already specific.

  
  

• E.g. Just a phone number a really hot girl gave me. The lovely Amanda gives me her phone number and I go and drop it.

When do we use the definite article "the"?

• Used to refer to things the speakers already know about. The things they know of is already specific.

  
  

• E.g. Just a phone number a really hot girl gave me. The lovely Amanda gives me her phone number and I go and drop it.

Definite article "the"

• Used with plural and singular nouns. E.g. I saw two houses. The houses were beautiful.

• Before the names of rivers, groups of islands, seas, oceans, and mountain ranges. E.g. The Everest is the highest mountain in the world.

  
  

• Before the names of certain public institutions and most newspapers. E.g. The Tambo Quirquincho museum is worth visiting.

• With acronyms, when each letter is pronounced individually. E.g. The USA is one of the biggest countries in the world.

No article (0) used for ...

• Things in general. E.g. I love reading books.

• Names: holydays, countries, companies, single lakes, languages and proper nouns: E.g. I love Christmas and speak English when I travel to the United States.

• Abstract nouns: love, hate, anger, happiness. E.g. Happiness is what I want for you.

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For more practice

https://www.myenglishpages.com/english/grammar-exercise-articles-2.php

https://www.youtube.com/watch?v=W_PSWOiXXuA