A and an are indefinite articles used to refer to a singular countable noun. These articles are used to refer to any member of a group or class. The speaker doesn’t tell us exactly which one he or she is referring to.
Use a/an for naming a member of a group:
- Mrs. Doudtfire is a nanny / Oscar works as an engineer (Jobs).
- Diego Armando Maradona is an Argentine (Nationalities).
- Barbara is a Jewish (Religions).
1) “A” is used before a consonant (b, c, d, etc.)
- a car.
- a dog.
- a Friday.
- a tiny nose.
- a 15 year-old boy.
- a year / week (time).
- a kilo / mile (measurements). Also using “one” instead of “a” is correct.
2) “A” is used before a vowel but consonant sound
- a university. [juː]
- a unit. [juː]
- a European. [jʊ]
- a one (1). [w]
3) “A” is used before a pronounced “h”
- a horse.
THE USE OF THE INDEFINITE ARTICLE “AN”
1) “An” is used before a vowel (a, e, i, etc.)
- an orange.
- an eye.
- an alligator.
2) “An” is used before an unpronounced (mute) “h”
- an hour [a].
- an honest [ˈɑ] (N. Amer.) - [ˈɒ] (Brit.)
- an honor [ˈɑ] (N. Amer.) - [ˈɒ] (Brit.)
- an heir [ɛ] (N. Amer.) - [e] (Brit.)
- an herb [ɜ] (N. Amer.)
3) “An” is used before a consonant but vowel sound
- an “F”. [ε]
- an MBA. [ε]
The is a definite article used to refer to something specific (singular or plural nouns). The speaker talks about a particular (or known) member of a group.
- The book on the table is about horror stories.
- Could you pass me the sugar, please?
- The movie was great.
THE USE OF THE DEFINITE ARTICLE “THE”
1) “The” is used before a noun which has already been previously mentioned
- I lost the wallet you gave me yesterday.
- They have a dog and two cats. The dog is Siberian husky.
2) “The” is used to indicate a noun that is unique or there is only one
- The President of United States lives in the White House.
- The Eiffel tower was built in 1889 to commemorate the French Revolution.
- The Nile is a river in Africa.
- Where is the bathroom?
3) “The” is used before superlative adjectives
- It’s the largest river in the world.
- She is the most beautiful lady of all time.
4) “The” is used to talk about the whole population of a country or region
- The British drink too much tea.
- The Romans invaded Britain in AD 43.
- The Mayans were famous for their architecture and astronomical knowledge.
HOWEVER: When generalizing about nationalities or a group of people, “the” is not usually used: “Americans eat a lot of hamburgers”
5) “The” is used to indicate all the members of a family
- The Simpsons live in Springfield.
6) “The” is used to talk about musical instruments
- She plays the piano every day.
7) “The” is used to talk about directions (cardinal points)
- the north.
- the south-east.