THE SHORT LIST OF RULES: Common Use of Articles

• "a/an" usually indicates an item in general or a typical item.
Example:A man and a boy are on a bus.

• "the" usually indicates one or more items that are specific or unique.
Example:The sun and the planets remain a mystery.

• "a/an" is used for the first mention of an item, followed by "the" for the second mention of the item.
Example: They took a train to Reno. The train was very clean and comfortable.

• "the" can be used with a first mention of an item only if the item is familiar to both the speaker and the listener.
Example: "Honey, where did you park the car?" "In the driveway, dear."

• "the" is used with nouns preceded by numbers or superlatives.
Example: The four friends sing folk songs. Really? What is the most popular song that they sing?

• "a" or "an" ?
Use "a" before words that begin with a consonant (or "u" when it is pronounced like "you"); use "an" before words beginning with a vowel (or with a "silent h").
Examples: " An eye for an eye, a tooth for a tooth." "A historian gave us a history lesson." "It was an honorable thing to do." "She teaches at a university."

THE LONG LIST OF RULES

DEFINITE ARTICLE - “THE”
Articles in English don’t change. They are the same for any gender or number of people or things: the girl, the man, the children, the cats, the cars
When to use 'the'

1. Use “the” with something which has already been mentioned so that both the speaker and listener know what is being talked about
There is an apple and a banana in the fruit bowl.
The apple is red and the banana is yellow,

2. Use “the” when both the speaker and listener know what is being talked about, even if it has not been mentioned before.
“ Where's the bathroom?”
“ It's just down the hall.”

3. Use “the” in sentences or clauses where we identify a specific person or object:
The woman who painted this picture is famous.
“ Which shirt did you choose?” “The blue one.”
“ My car is the one parked in front.”

4. Use “the” to refer to things that are unique:
the sun, the moon, the world

5. Use “the” before superlatives and ordinal numbers:
the highest mountain, the smallest child
the first page, the third book, the last chapter.

6. Use “the” with adjectives, to refer to a whole group of people:
Examples: the Italians, the Irish, the working class, the poor

7. Use “the” with names of geographical areas and with oceans:
Examples: the Caribbean, the Middle East, the Pacific, the Atlantic

8. Use with decades, or groups of years:
Example: my teacher grew up in the sixties; jazz became popular in the 1920’s

INDEFINITE ARTICLE – “A” / “AN”
Use 'a' with nouns starting with a consonant (letters that are not vowels),

'an' with nouns starting with a vowel (a,e,i,o,u)
Examples:
A boy
An apple
A car
An orange
A house
An opera
Exceptions:
An before an h when it is not pronounced - an hour, an honour.
A before u and eu when they sound like 'you': a european, a university, a unit

The indefinite article is used:
• When you mention something for the first time:
Two birds, an eagle and a hawk, were flying high in the sky.
Would you like a cup of coffee?
I've got a good class.

• When you refer to a particular person or thing in a group or class
Examples:

• with names of jobs:
John is a doctor.
Mary is training to be an engineer.
He wants to be a dancer.

• with nationalities and religions:
John is an Englishman.
Kate is a Catholic.

• with musical instruments:
Sherlock Holmes was playing a violin when the visitor arrived.
(BUT to describe the activity we say "He plays the violin.")

• with names of days:
I was born on a Thursday

• When you refer to a kind of, or example of something:
the mouse had a tiny nose
the elephant had a long trunk
it was a very strange car

• With singular nouns, after the words 'what' and 'such':
What a shame!
She's such a beautiful girl.

• When the meaning is 'one', referring to a single object or person:
I'd like an orange and two lemons please.
The burglar took a diamond necklace and a valuable painting.
Notice also that we usually say a hundred, a thousand, a million.
NOTE: that we use 'one' to add emphasis or to contrast with other numbers:
I don't know one person who likes eating elephant meat.
We've got six computers but only one printer.

EXCEPTIONS TO USING THE DEFINITE ARTICLE
There is NO article used:
• With names of countries (if singular)
Germany is an important economic power.
He's just returned from Zimbabwe.
(But: I'm visiting the United States next week.)

• With the names of languages
French is spoken in Tahiti.
English uses many words of Latin origin.
Indonesian is a relatively new language.

• With the names of meals.
Lunch is at midday.
Dinner is in the evening.
Breakfast is the first meal of the day.

• With people's names (if singular):
John's coming to the party.
George King is my uncle.
(But: we're having lunch with the Morgans tomorrow.)

• With titles and names:
Prince Charles is Queen Elizabeth's son.
President Kennedy was assassinated in Dallas.
Dr. Watson was Sherlock Holmes' friend.
(But: the Queen of England, the Pope.)

• After the 's possessive case:
His brother's car.
Peter's house.

• With professions:
Engineering is a useful career.
He'll probably go into medicine.

• With names of shops:
I'll get the card at Smith's.
Can you go to Boots for me?

• With years:
1948 was a wonderful year.
Do you remember 1995?

• With uncountable nouns:
Rice is the main food in Asia.
Milk is often added to tea in England.
War is destructive.

• With the names of individual mountains, lakes and islands:
Mount McKinley is the highest mountain in Alaska.
She lives near Lake Windermere.
Have you visited Long Island?

• With most names of towns, streets, stations and airports:
Victoria Station is in the centre of London.
Can you direct me to Bond Street?
She lives in Florence.
They're flying from Heathrow.

• With some fixed expressions, for example:
by car
by train
by air
on foot
on holiday
on air (in broadcasting)
at school
at work
at University
in church
in prison
in bed

The "long list" is adapted from article use rules on EduFind.com