There are two main articles in the English language – a and the. A variant to the first article is an, which is used before words that begin with vowels.
Articles are used before nouns, and just like adjectives (also used before nouns), articles also modify nouns.
Know what modify means? It means ‘to change’ in some way or another.
Let’s look at an example,
I saw a cat. I saw an otter.
I saw the cat.
In the first sentence, I’m referring to a cat that I saw. It may have been any cat. I’m not being specific.
In the second sentence, I’m referring to a particular cat that I saw. I’m being specific.
That’s why a and an are called indefinite articles. And the is called a definite article.
There is a corresponding ESL lesson plan on articles on the blog. Check it out, if you’re an ESL teacher and looking for a nudge of inspiration 
