Singular count nouns cannot stand alone in a sentence.
Apple is on table. (Wrong!)
They must be preceded by one of the following:
1. An article (the, a, an)
An apple is on the table.The professor gave us a test.
2. A number or quantifier (one, another, the other, each, every, either, neither)
One man was in Chicago.Neither man was with his wife.
The other man was in Saint Paul.Either man could be in trouble.
Note: Never use the and another, each, every, neither, either together:
The another man was in Milwaukee. (Wrong!)
3. This, that, some*
This artist created that painting.Some woman came to see you. (*unidentified subject)
4. A possessive pronoun or noun.
It is my bicycle now.It was John's bicycle.
Note: Do not use articles and possessives together.
The Mary's bicycle was stolen. (Wrong!)
Proper nouns have their own article usage.
Don Smith lived next door to Dr. Zimbango.The Empire State Building is in New York City.
Non-count and plural nouns can be used without articles only in the ?generic? sense:
Cats are enemies of dogs.Water is essential for survival.