A comma (,) usually indicates a pause between parts of a sentence. It is also used to separate items in a list. 

Rules for using commas

  1. Use a comma when a series of two or more adjectives modify a noun.
    • Sal’s band plays loud, abrasive, complex music.
  2. Use a comma to separate three or more items in a series.
    • Anna’s grandmother is good at making fudge, nursing hurt animals, tending fruit trees, telling stories, and playing Scrabble.
  3. Use a comma before a coordinating conjunction (for, and, nor, but, or, yet, so) that joins two complete sentences.
    • Glenn was craving Krispy Kreme donuts, but he knew it was a bad idea to eat too much sugar before going to bed.
  4. Use a comma after material that introduces a complete sentence.
    There are six types of introductory clauses:
    • Dependent Word or Phrase
      • Additionally, I don't plan to go to the party tonight either.
      • Since my parents enjoy watching movies, they go every weekend.
    • Preposition
      • In Mexico, the Day of the Dead is a traditional holiday. 
    • Infinitive verb (“to” + verb)
      • To learn ballroom dancing correctly, you should take lessons. 
    • Past Participle
      • Walking home from school, the young boy found a fifty-dollar bill. (Present participle)
    • Signal Verb
      • Dr. King said, “At the center of non-violence stands the principle of love.” (Signal verb)
    • Transitional Word
      • Elaine caught the flu. Therefore, she had to miss her cousin’s wedding. (Transitional word)
  5. Use commas around a “nonessential clause."
    A “nonessential clause” is material that is extra information and does not change the meaning of the sentence when taken out. 
    • My brother, who is single, lives in New York City. (nonessential)
    • My brother who is single lives in New York City. (essential)
  6. Use commas to set off information that “interrupts” the flow of a sentence.
    Interrupters can be emotional interjections (oh, well, wow), parenthetical expressions (to be exact, in fact, it seems), and transitional words (moreover, however, therefore).
    • People think my English accent sounds fake. My girlfriend, however, thinks it’s attractive. 

When NOT to use a comma

  1. Do not use a comma between 2 independent clauses. A comma cannot separate independent clauses and either a period or a semicolon should be used or a conjunction added. 
    • Incorrect: Sal’s band plays loud music, it hurts my ears.
    • Correct: Sal's band plays loud music. It hurts my ears.
    • Correct: Sal's band plays loud music; it hurts my ears.
    • Correct: Sal's band plays loud music and it hurts my ears.
  2. Do not use a comma to separate 2 actions of the same subject
    • Incorrect: Anna’s grandmother made fudge, and sent it to Anna.
    • Correct: Anna's grandmother made fudge and sent it to Anna.
  3. Do not use a comma to separate 2 subjects performing the same action. This is a compound subject, which acts as a single subject.
    • Incorrect: Glenn, and Xavier were craving Krispy Kreme donuts.
    • Correct: Glenn and Xavier were craving Krispy Kreme donuts.
  4. Do not use a comma to indicate a list follows. A colon should be used to indicate a list follows.
    • Incorrect: My qualifications include,  
      • Time management
      • Attention to detail
    • Correct: My qualifications include:
      • Time management
      • Attention to detail
  5. Do not use a comma to separate a single adjective from the noun it modifies. A comma should be used to separate 2 or more adjectives or adverbs used to modify a noun.
    • Incorrect: When traveling, I miss my affectionate, dog.
    • Correct: When traveling, I miss my affectionate dog.
    • Incorrect: When traveling, I miss my silly affectionate dog.
    • Correct: When traveling, I miss my silly, affectionate dog.
  6. Do not use a comma to separate an adverb from an adjective where both are modifying the same noun.
    • Incorrect: My husband has unusually, large hands.
    • Correct: My husband has unusually large hands.