• It refers to something previously mentioned: "The reading you did for today's class".
• It stands for all other items of its type: "Bell Labs invented "the transistor."
• It is identified by a special marker adjective, such as
  • a superlative: the biggest test of the semester, the most important point
  • a particular (ordinal) number: the second semester, the 50^th aniversary
  • a proper or distinctive name [usually]: The United States ( but Canada), the registrar's office, the 486 chip
• It refers to a time or place we treat as a collective unit: the sixties, the earth, the golden years
• It is followed by modifiers, especially relative clauses of "of" phrases: the dean who wrote the letter, the office in charge of admissions
• It refers to knowlege the writer/speaker and audience share: the group project, the next home game
• It refers to a particular object, even if the reader doesn't yet know it's particular: Plug the mouse into the socket on the back of the computer.

What Makes a Noun Something You Can Count?

• It is readily found in plurals: memos, students, tests, but not researches, waters
• It occurs readily with numbers: five class meetings, 238 casualties, 48500 workers
• It occurs with words that suggest numbers: few drawbacks, most classes, many jobs

What Makes a Noun Something You Cannot Count?

• It refers to physical mass without distinct form or shape: water, ROM, sand, fat, neon
• It refers to an absract concept: gravity, information, justice, satisfaction, apartheid
• It refers to ongoing processes: research, growth, pollution, communication, tutoring
• It refers to a field of study or endeavor: engineering, optics, materials, science, baseball

Do Not Use an Article With a Proper Noun When

• the noun is a common noun used as a term of address: Father, Reverend, Professor
• the noun is an acronym that you pronounce as a word: NATO, UNIX, DOS

• The proper noun is used to indicate characteristicsof the named person: He's a real Rambo in negotiations, isn't he?
• the noun means "a certain person whose name is": "An Ed Clinton called last night."

• The proper noun refers to surnames in the plural: The Martinezes are moving.
• You are distinguishing between people with the same name: The Mike Jordan I know isn't the athlete Michael Jordan.

• The noun is part of an accepted geographical name (there's no reason, just custom, to most of these--check the examples as well as the definition in your dictionary)
  

  the Philippines	the USSR	the Red Sea	the West
  the Mississippi	the Great Lakes	the continent	the Alps
  the University of Virginia	the Atlantic and Pacific Oceans



• The article is part of an accepted proper name, such as a ship, newspaper, desert, group or organization, hotel, etc. (you may have to check a dictionary or print example for these).
  

  the Hilton	The Beatles	The New York Times	the Titanic
  the United Nations	the Super Bowl	the Sahara	The Grateful Dead



• The word is an acronym whose letters are separately pronounced (but watch those tricky exceptions):
  

  the U.N.	The U.S.A.	the F.B.I	the I.N.S.
  but
  I.B.M.	UPS	A.T. & T.	UCLA	MIT	RCA	G.M.