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. If the information is essential, then remove the commas. 
    • Nonessential: My brother, who is single, lives in New York City.
      • In this case, the writer has 1 brother, and he lives in NYC. The fact that he is single is extra information that is added for emphasis but is not essential to make it a complete sentence. 
    • Essential: My brother who is single lives in New York City.
      • In this case, the writer has more than 1 brother, and the "brother who is single" is the one living in NYC. To maintain meaning, it is essential to distinguish this brother from others. 
  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. Instead, use either a period or a semicolon. The exception is when you use a comma-conjunction to join 2 independent clauses (for, and, nor, but, or, yet, so): 
    • 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 Exception: 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 craved Krispy Kreme donuts.
    • Correct: Glenn and Xavier craved 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.