This gentle punctuation mark(,) the comma, is used inside sentences to separate or set apart words, phrases, or clauses to make things clear. Commas often come in pairs. Here are some of the most frequent uses of the comma in sentences.

Use a comma:

• Between independent clauses joined by these coordinating conjunctions: for, and, nor, but, or, yet, so.
  
  

  It takes me only 25 minutes to drive to the college, but I have to allow another ten minutes to find a parking place.

  
  

• unless the clauses are very short.
  
  

  She walked and he ran.
  
  

• To set off introductory words, phrases, and clauses that come before the subject.
  
  

  When I was walking to school, I saw an auto accident. (Clause)

  While walking home, I saw another one. (Phrase)

  Fortunately, nobody was hurt in either one. (Word)
  
  

• unless it is very short.
  
  

  Yesterday I mowed the lawn.
  
  

• To separate items in a series of three or more or two or more adjectives modifying the same noun.
  
  

  She offered them apples, pears, bananas, and grapes. (Nouns)

  He liked to swim, hike, ski, and hunt. (Verbs)

  The long, hot, rainless summer damaged the apple crop. (Adjectives)
  
  

• (Note: some experts use a comma before and; some don't. The current trend seems to be to use it, but clarity is primary.)
  
  
• To set off words in direct quotation.
  
  

  He said, "I will never agree to that."

  "Sixteen people are coming to the party," Mary told her friends.
  
  

• To set off interrupting elements or extra material anywhere in the sentence.
  
  

  John, please close the door when you leave. (Name in direct address)
  
  

  Abraham Lincoln, the sixteenth president of the United States, issued the Emancipation Proclamation in 1863. (Appositive)
  
  

  Well, that's over. (Mild exclamation)
  
  

  The cake, ablaze with 90 candles, was placed on the table in front of Grandmother. (Descriptive modifier, nonrestrictive)
  
  

  He still had doubts, however, and asked for more information. (Adverbial conjunction)
  
  

  The government, in my opinion, is overreacting to what is, in reality, a minor matter. (Parenthetical expressions)
  
  

  John Pembroke, Ph.D., will speak in the auditorium at noon on Friday. (Title)
  
  

  You enjoyed that book, didn't you? (Tag-end question)

Do not use a comma:

• With "that" clauses; with restrictive who, whom, whose, and which clauses; or with phrases containing essential information.
  
  

  The dog that bit the postman was destroyed.
  
  

  The hand that rocks the cradle rules the world.
  
  

  The man whose coat was stolen threatened to sue the restaurant.
  
  

  The dress which she bought needs to be shortened.
  
  

  The cookies made with real butter tasted best.
  
  

• Between main parts of a sentence. (Subject-verb-completer)
  
  

  The storm blew down trees and caused many power failures.

  
  

• Between two items joined by and or or.
  
  

  Salt and pepper are the only seasonings she uses.

Miscellaneous:

• When used in a sentence, years and states need a comma before and a comma after.
  
  

  On July 4, 1776, in Philadelphia, Pennsylvania, the Continental Congress adopted the Declaration of Independence.
  
  

• Commas may also be used when necessary to clarify a sentence.
  
  

  The question is, is it true?
  
  

  OK, we'll come now, and then go.