Use of the articles a, an, and the depends on whether the noun following the article possesses these paired qualities: countable vs. noncountable, definite vs. indefinite, first vs. subsequent mention, and general vs. specific. These topics, as well as the meanings associated with the nonuse or omission of articles, are covered in the following sections of this document:
A and an are used if the noun can be counted.
I ran into a post. (How many posts did you run into? Just one. Therefore, use a.)
I ate a piece of cake.
I saw an eagle.
The is used when the noun cannot be counted.
I ran into the water. (How many waters did you run into? The question doesn't make any sense because water is noncountable. Therefore, use the.)
I ate the rice.
I saw the milk spill.
A and an signal that the noun modified is indefinite, referring to any member of a group. These indefinite articles are used with singular nouns when the noun is general; the corresponding indefinite quantity word some is used for plural general nouns. The rule is:
a + a singular noun beginning with a consonant: a boy
an + a singular noun beginning with a vowel: an elephant
some + a plural noun: some girls
Note that in English, the indefinite articles are used to indicate membership in a profession, nation, or religion.
I am a teacher.
Brian is an Irishman.
Seiko is a practicing Buddhist.
The definite article is used before singular and plural nouns when the noun is particular or specific. The signals that the noun is definite, that it refers to a particular member of a group. Compare the indefinite and definite articles in the following pairs:
A dog (any dog)
The dog (that specific dog)A book (any book)
The book (that specific book)
The is used with both singular and plural nouns:
the book, the cat
the books, the cats
The is not used with noncountable nouns referring to something in a general sense:
[no article] Coffee is a popular drink.
[no article] Japanese was his native language.
[no article] Intelligence is difficult to quantify.
The is used with noncountable nouns that are made more specific by a limiting modifying phrase or clause:
The coffee in my cup is too hot to drink.
The Japanese he speaks is often heard in the countryside.
The intelligence of animals is variable but undeniable.
The is also used when a noun refers to something unique:
the White House
the theory of relativity
the 1999 federal budget
Do not use the before:
names of countries, except the Netherlands and the US (Italy, Mexico, Bolivia)
names of cities, towns, or states (Seoul, Manitoba, Miami)
names of streets (Washington Blvd., Main St.)
names of lakes and bays, except with a group of lakes like the Great Lakes (Lake Titicaca, Lake Erie)
names of mountains, except with ranges of mountains like the Andes or the Rockies or unusual names like the Matterhorn (Mount Everest, Mount Fuji)
names of continents (Asia, Europe)
names of islands except with island chains like the Aleutians, the Hebrides, or the Canary Islands (Easter Island, Maui, Key West)
Do use the before:
names of rivers, oceans and seas (the Nile, the Pacific, the Sea of Japan)
points on the globe (the Equator, the North Pole)
geographical areas (the Middle East, the West)
deserts, forests, gulfs, and peninsulas (the Sahara, the Persian Gulf, the Black Forest, the Iberian Peninsula)
A or an is used to introduce a noun when it is mentioned for the first time in a piece of writing. The is used afterward each time you mention that same noun.
An awards ceremony at the Kremlin would not normally have attracted so much attention. But when it was leaked that Soviet President Konstantin Chernenko would be presenting medals to three cosmonauts, interest in the ceremony intensified. Time, Sept. 17, 1984.
Note: There is and there are can be used to introduce an indefinite noun at the beginning of a paragraph or essay.
A, an, and the can all be used to indicate that a noun refers to the whole class to which individual countable nouns belong. This use of articles is called generic, from the Latin word meaning "class."
A tiger is a dangerous animal. (any individual tiger)
The tiger is a dangerous animal. (all tigers: tiger as a generic category)
The difference between the indefinite a and an and the generic a and an is that the former means any one member of a class while the latter means all of the members of a class.
The omission of articles also expresses a generic (or general) meaning:
no article with a plural noun: Tigers are dangerous animals. (all tigers)
no article with a noncountable noun: Anger is a destructive emotion. (any kind of anger)
While some nouns combine with one article or the other based on whether they are countable or noncountable, others simply never take either article. Some common types of nouns that don't take an article are:
Chinese
English
Spanish
Russian
volleyball
hockey
baseball
mathematics
biology
history
computer science
This page is located at http://owl.english.purdue.edu/handouts/esl/eslart.html
on With days:
on Monday
on Sunday
at With noon, night, midnight, with the time of day:
at noon
at 6 p.m.
in With other parts of the day, with months, with years, with seasons:
in the afternoon
in August
in 1999
in spring
since yesterday
for two weeks
from August to October
from spring until fall
during the evening
within a year
in the room
inside the box
on the table
at the corner
over the roof
above the window
under the ground
underneath the blanket
beneath the branches
below eye-level
near the street
by the store
next to my house
between Elm Street and Maple Street
among the books
opposite that room
glance at her mirror
laugh at his joke
look at the computer monitor
approve of his speech
consist of many pages
smell of alcohol
dream of finishing college
think of a problem
call for an order
hope for a raise in salary
look for the moon
wait for her
watch for the train
wish for an "A
http://owl.english.purdue.edu/handouts/esl/eslprep4.html