the = definite article
a/an = indefinite article
For example, if I say, "Let's read the book," I mean a specific book. If I say, "Let's read a book," I mean any book rather than a specific book.
Here's another way to explain it: The is used to refer to a specific or particular member of a group. For example, "I just saw the most popular movie of the year." There are many movies, but only one particular movie is the most popular. Therefore, we use the.
"A/an" is used to refer to a non-specific or non-particular member of the group. For example, "I would like to go see a movie." Here, we're not talking about a specific movie. We're talking about any movie. There are many movies, and I want to see any movie. I don't have a specific one in mind.
Let's look at each kind of article a little more closely.
INDEFINITE ARTICLES: A AND AN
"A" and "an" signal that the noun modified is indefinite, referring to any member of a group. For example:
- "My daughter really wants a dog for Christmas." This refers to any dog. We don't know which dog because we haven't found the dog yet.
- "Somebody call a policeman!" This refers to any policeman. We don't need a specific policeman; we need any policeman who is available.
- "When I was at the zoo, I saw an elephant!" Here, we're talking about a single, non-specific thing, in this case an elephant. There are probably several elephants at the zoo, but there's only one we're talking about here.
REMEMBER, USING A OR AN DEPENDS ON THE SOUND THAT BEGINS THE NEXT WORD. SO...
- a + singular noun beginning with a consonant: a boy; a car; a bike; a zoo; a dog
- an + singular noun beginning with a vowel: an elephant; an egg; an apple; an idiot; an orphan
- a + singular noun beginning with a consonant sound: a user (sounds like 'yoo-zer,' i.e. begins with a consonant 'y' sound, so 'a' is used); a university; a unicycle
- an + nouns starting with silent "h": an hour
- a + nouns starting with a pronounced "h": a horse
- In some cases where "h" is pronounced, such as "historical," you can use an. However, a is more commonly used and preferred.A historical event is worth recording.
Remember that these rules also apply when you use acronyms:
Another case where this rule applies is when acronyms or initialisms start with consonant letters but have vowel sounds:
If the noun is modified by an adjective, the choice between a and an depends on the initial sound of the adjective that immediately follows the article:
- a broken egg
- an unusual problem
- a European country (sounds like 'yer-o-pi-an,' i.e. begins with consonant 'y' sound)
Remember, too, that in English, the indefinite articles are used to indicate membership in a group:
- I am a teacher. (I am a member of a large group known as teachers.)
- Brian is an Irishman. (Brian is a member of the people known as Irish.)
- Seiko is a practicing Buddhist. (Seiko is a member of the group of people known as Buddhists.)
DEFINITE ARTICLE: THE
The definite article is used before singular and plural nouns when the noun is specific or particular. The signals that the noun is definite, that it refers to a particular member of a group. For example:
"The dog that bit me ran away." Here, we're talking about a specific dog, the dog that bit me.
"I was happy to see the policeman who saved my cat!" Here, we're talking about a particular policeman. Even if we don't know the policeman's name, it's still a particular policeman because it is the one who saved the cat.
"I saw the elephant at the zoo." Here, we're talking about a specific noun. Probably there is only one elephant at the zoo.
COUNT AND NONCOUNT NOUNS
The can be used with noncount nouns, or the article can be omitted entirely.
- "I love to sail over the water" (some specific body of water) or "I love to sail over water" (any water).
- "He spilled the milk all over the floor" (some specific milk, perhaps the milk you bought earlier that day) or "He spilled milk all over the floor" (any milk).
"A/an" can be used only with count nouns.
- "I need a bottle of water."
- "I need a new glass of milk."
Most of the time, you can't say, "She wants a water," unless you're implying, say, a bottle of water.
GEOGRAPHICAL USE OF THE
There are some specific rules for using the with geographical nouns.
Do not use the before:
- names of most countries/territories: Italy, Mexico, Bolivia; however, the Netherlands, the Dominican Republic, the Philippines, the United States
- names of cities, towns, or states: Seoul, Manitoba, Miami
- names of streets: Washington Blvd., Main St.
- names of lakes and bays: Lake Titicaca, Lake Erie except with a group of lakes like the Great Lakes
- names of mountains: Mount Everest, Mount Fuji except with ranges of mountains like the Andes or the Rockies or unusual names like the Matterhorn
- names of continents (Asia, Europe)
- names of islands (Easter Island, Maui, Key West) except with island chains like the Aleutians, the Hebrides, or the Canary Islands
Do use the before:
- names of rivers, oceans and seas: the Nile, the Pacific
- 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
OMISSION OF ARTICLES
Some common types of nouns that don't take an article are:
- Names of languages and nationalities: Chinese, English, Spanish, Russian (unless you are referring to the population of the nation: "The Spanish are known for their warm hospitality.")
- Names of sports: volleyball, hockey, baseball
- Names of academic subjects: mathematics, biology, history, computer science