What are articles?
Articles are special modifiers that appear before nouns or noun phrases. Like other adjectives, they help clarify the meaning of the noun in your sentence. There are only two articles in the English language: the and a (and its variant an, used before a word that starts with a vowel sound). A noun may also appear without an article in front of it. If you are a native speaker, you will probably know which article to place in front of a noun without having to think about it. If, however, English is your second language, knowing which article to use where can be difficult. Learning and consciously applying a few basic principles can help you improve your article use significantly. With time and a lot of practice, using articles correctly will become second nature.
Where exactly do articles go?
Articles belong in front of all other modifiers preceding a noun:
a large urban university
the first female college principal
There are other special modifiers called determiners or markers that may appear in front of a noun phrase. Do not use an article if you also intend to use any of the following markers directly before the noun: this, that, these, those, my, his, her, your, our, their, its, any, either, each, every, many, few, several, some, all.
A useful set of rules for using articles
You can determine which article to place in front of almost any noun by answering the following three questions: Is the noun countable or uncountable? Is it singular or plural? Is it definite or indefinite?
A noun is countable if you can have more than one instance of it. The word exam is countable because you can have, say, four exams scheduled at the end of the year. The word concentration, however, is uncountable, because it would not make sense to speak of having four concentrations, even though you will need a lot of concentration to study for all four exams. Many words have both countable and uncountable meanings, depending on the sentence.
Knowing whether the particular use of a noun is singular or plural is quite straightforward. Just ask the question, Am I referring to more than one instance of something?
A noun is definite when it is clear to your reader which specific instance or instances of an entity you are referring to; otherwise it is indefinite. Often the first use of a noun is indefinite and subsequent uses are definite.
When I started university, I had a phobia about exams. I conquered the phobia by writing lots of them.
Here, the first sentence establishes for the reader the existence of the writer's former phobia. By the second sentence, the reader knows exactly which phobia the writer is talking about—the one about exams just referred to in the previous sentence. The first use of a noun can be definite if the reader can figure out from context or some other clue just which instance of an entity the writer is referring to.
The point of my professor's exams was to make sure we understood the course material.
Note that the prepositional phrase following point narrows down its meaning to something very specific, while the course material can refer only to the material in this particular professor's course. Both nouns are therefore definite.
Once you have answered all three questions, you can use the following chart to help you choose the correct article. (The symbol Ø means no article.)
definite indefinite singular the
e.g. I need to study hardest for the exam that I write next Wednesday.
e.g. I have an exam to write this afternoon, and then my summer holiday finally begins.
e.g. The exams that I wrote last year were much easier.
e.g. Exams are an inescapable fact of life for most university students.
definite indefinite singular the
e.g. The importance of studying hard cannot be exaggerated.
e.g. Do not attach importance to memorizing facts.
Observe the following: If the noun is definite, it always takes the article the; if the noun is indefinite it never takes the article the. If you don't have the chart in front of you, you can still often get the article right just by remembering that simple rule of thumb.
Using articles to refer to classes of objects
Nouns can refer to an entire group of similar objects, sometimes called a class. There are three ways to refer to a class: using (1) the definite singular, (2) the indefinite singular, or (3) the indefinite plural. Here is an example of each:
(1) The lion is a majestic animal.
(2) A lion is a majestic animal.
(3) Lions are majestic animals.
All three sentences convey the same meaning with slightly different emphasis. The first sentence takes one lion as a representative of all lions and then makes its assertion about that representative. The second sentence in effect states, take any lion you like from the class of all lions, and what you say about it will be true of all other lions. The third sentence directly makes its assertion about all lions. This third usage is probably the most common. Choose whichever usage sounds best in your sentence.
Using articles in front of proper nouns
The rules in the chart do not work in all situations. In particular, they are not much help in the case of proper nouns. Most proper nouns, however, are governed by simple rules. For example, do not place an article in front of the names of people.
Stephen Harper is the twenty-second prime minister of Canada.
Most countries, like Canada in the sentence above, do not take articles. Here are two noteworthy exceptions: the United States, and the United Kingdom. Rivers, mountain ranges, seas, and oceans should be preceded by the article the: the Amazon River, the Rocky Mountains, the Ural Sea, the Pacific Ocean. Lakes, on the other hand, don't usually take an article: Lake Louise, Lake Ontario.
Find out more about articles by visiting the University of Toronto's page on special cases in the use of the definite article.