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The serial comma is used in a series of elements. Use a comma in a series and before the final "and" or "or."

  • As a freshman, he took courses in writing, English, biology, and math.
  • Hmm, shall I have the grilled swordfish, barbecued spareribs, or Irish stew?
  • After work, he picked up his shirts at the cleaners, went to the ATM, and met his wife.

Place a comma after digits signifying thousands (3,400 students), except when referring to temperature or year (4600 degrees, in the year 2001).

Transition terms, such as "however," "namely," "i.e." (that is), and "e.g." (for example), should be immediately preceded by a comma or semicolon and followed by a comma:

  • Our evening class is three hours long; however, we do take a 15-minute break.
  • We have a lengthy assignment, namely, chapters one, two and three.

Use a comma before coordinate adjectives; apply the following test:

Place the word and between the adjectives. Second, reverse them. If, in both instances, the resulting phrase still sounds appropriate, you likely have coordinate adjectives and should use a comma between them.

  • Students attended a lengthy, informative planning session.
  • The lecture will present multiple cost-effective strategies.
  • A confident, knowledgeable panelist gave a quick rebuttal.

Do not use a comma in names ending in "Jr." or a numeral (III):

  • John Smith Jr.
  • John F. Zeller III

When writing a date or a location with city and state, place a comma after any element preceded by one:

  • On July 4, 1976, the nation celebrated its 200th birthday.
  • Located in West Hartford, Conn., the University of Hartford comprises seven schools and colleges.

Do not place a comma between the month and year when the day is not mentioned:

  • July 2007

Use of a comma in the following situations will depend on your additional knowledge of the situation and/or how the sentence is worded.

  • My sister, Helen, is on vacation. (If you have just one sister since this is a unique identifier)

  • My sister Helen is on vacation. (if you have more than one sister)
  • I went to see Woody Allen's movie Midnight in Paris with my friend Bill. (we know Woody Allen has been in dozens of movies and we are assuming that Bill is not your only friend)
  • I went to see my favorite Woody Allen movie, Midnight in Paris, with my oldest friend, Bill. (commas in play in both cases as you have only one "favorite" Woody Allen movie, and before "Bill" because he and only he is your oldest friend)