There are two types of articles:
Definite articles: refer to specific things (“the”)
Indefinite articles: refer to general things in their singular form (“a” and “an”)
The word “the” is called the definite article. It is used when talking about a specific person, place or thing—something that both the speaker and listener know about. For example:
Please pass me the salt.
I want the hat on the left.
I saw the neighbor’s cat in your garden.
The words “a” and “an” are called indefinite articles. They are used when talking about something that is not specific or something that the listener may not know about. For example:
I saw a dog in the park.
She ate an apple for lunch.
He wants to buy a car.
The choice between “a” and “an” depends on the sound that begins the word following the article.
Use "a" before words starting with a consonant sound: a car, a teacher, a university
Even though “university” starts with the letter "u," it makes a "y" sound, like “you,” which is a consonant sound.
Use "an" before words starting with a vowel sound (a, e, i, o, u): an apple, an elephant, an hour
Even though “hour” starts with the letter "h," it is silent, so the word begins with a vowel sound.
There are times when we do not use articles in English. These are called zero articles. We generally do not use articles:
Before plural nouns or uncountable nouns (when talking in general): When talking about things in general, you do not need an article before plural nouns or uncountable nouns (things that cannot be counted). For example:
I love dogs.
She likes music.
Water is important for life.
Before proper nouns: We do not use articles with most proper nouns, such as the names of people, places or specific things. For example:
I live in London.
We visited Mount Everest.
I have an appointment with Dr. Smith.
Exception: Some proper nouns take "the," such as “the United States,” “the Eiffel Tower,” and “the Pacific Ocean.”
