This page discusses some uses for commas, as well as common errors that writers make when using commas. 

Six Common Uses for Commas 

1. Introductory Phrases & Clauses 

Introductory phrases and clauses are groups of words that begin sentences. These groups of words contain neither the main subject nor main verb of the sentence, so it is important to set them apart from the independent clause of the sentence. An introductory phrase or clause can’t stand alone as a sentence. It must be connected to an independent clause with a comma. 

Intro phrases and clauses can be short (even just a single word): 

  • Generally, I don’t like Pop Tarts. 
  • Throughout his life, Immanuel Kant was thoroughly confused. 

Introductory phrases and clauses can also be longer. You can sometimes identify them by looking for prepositions like When, If, As, Although, and Because.

  • If John is successful in returning the movie without paying the late fee, we will never rent at Hollywood Video again. 
  • As you can see from my 40-page research paper, Albert Einstein loved to roller skate. 
  • Because a gang of thieves stole my car last night, I wasn’t able to drive to work. 

2. Joining Independent Clauses with FANBOYS 

Commas can also be used to join independent clauses—but not by themselves! Remember, two independent clauses joined by a comma is still a run-on sentence. To connect independent clauses, you need to use a comma and a coordinating conjunction, a.k.a. FANBOYS. Just in case you’ve forgotten, FANBOYS is the acronym For, And, Nor, But, Or, Yet, and So. Use any of these little connecting words with a comma to connect independent clauses in a sentence. 

  • I love disco dancing, but it seems like I’m the only one. 
  • Ivan lost his hat, so we went back to the mall to look for it.
  • That bass has been in my family for a long time, and I’m the only one who knows how to play it. 

3. Between Modifiers 

Modifiers are describing words. There are two main kinds: adjectives (words that describe a noun) and adverbs (words that describe a verb). If multiple modifiers describe the same word, a comma separates the modifiers. 

  • The old, broken hammer didn’t work very well. 
  • I spilled soda all over my new, expensive computer. 
  • I quickly, forcefully ate my snow cone. 

4. Lists

 When you have a list of three or more things in a sentence, you need commas between the things in your list. 

  • The Declaration of Independence guarantees life, liberty, and the pursuit of happiness. 
  • When I go camping, I always bring a book, a bean bag chair, and a can opener. 

5. Parenthetical Phrases 

Fancy grammar people, in their fancy grammar hats, call parenthetical phrases “Nonrestrictive Clauses.” But we’ll define a parenthetical phrase as extra information separate from the primary thought of the sentence. Some people call these phrases “interrupters” because they are set apart from the main sentence by commas and “interrupt” the man idea of the sentence. For example: 

The movie, which was three-hours long, turned out to be really good. 

The fact that the movie lasted three hours isn’t essential to the main idea of the sentence: that the movie was good. It’s extra information. Therefore, the writer set off the phrase with commas on either side of it. 

Sometimes setting off parenthetical phrases from the main sentence can really affect the meaning of the sentence. Consider: 

  • The employee who left work early avoided being stuck in the blizzard.
  • The employees, who left work early, avoided being stuck in the blizzard. 

In the first sentence, only the employees who left early avoided the blizzard. In the second, all of the employees avoided it. In this case, the commas tell the reader where the extra information in the middle of the sentence begins and where it ends. 

6. Quotations 

When you’re quoting someone, commas are your friends. Use them to set off quoted language in a sentence from the attribution (who is speaking the quoted language). You’ll notice, too, that commas (and periods) often go inside quotation marks. 

  • “To be, or not to be,” asked Hamlet.
  • “Your existential crisis is getting quite trite,” said his mother. 
  • Hamlet replied, “Fine. By the way, have you seen my sword?” 

Commas Gone Wrong! 

1. The comma splice 

The comma splice is a particular hazardous error because it’s very discombobulating for the reader. A comma splice occurs when the writer tries to join two independent clauses with only a comma (and no FANBOYS). The reader thinks they’re getting one thing—a dependent clause after the comma. But they’re actually getting a complete thought following the comma. 

  • INCORRECT: I really love grammar, it is my favorite thing. 
  • CORRECT: I really love grammar. It is my favorite thing. 

2. Rogue commas between subjects and verbs 

In English, you’ll almost never find a comma between a subject and its verb (and rarely between a verb and its object). The obvious exception, of course, is when you place two commas around a parenthetical phrase that appears between the two. Here are some dopey, silly examples:

  • INCORRECT: The very small walrus, ate his toast every Tuesday night. 
  • CORRECT: The very small walrus ate his toast every Tuesday night. 
  • INCORRECT: Bill threw the ball, to Jimmy. 
  • CORRECT: Bill threw the ball to Jimmy. 

3. Commas after independent clause when dependent clause follows it

When a dependent clause follows an independent clause (and it's closely related in subject), you don’t need to separate the two with a comma.

  • INCORRECT: He was looking at his phone, while he was driving. 
  • CORRECT: He was looking at his phone while he was driving. 
  • INCORRECT: Nora told me to relax, because I was kind of freaking out.
  • CORRECT: Nora told me to relax because I was kind of freaking out. 

Works Consulted

  • “Purdue OWL: Commas.” Purdue Online Writing Lab, 2017. https://owl.english.purdue.edu/owl/resource/607/01/. Accessed 1 March 2017. 
  • The Writing Center. The Writing Center at George Mason University, 2017. http://writingcenter.gmu.edu/. Accessed 1 March 2017.
  • UNC Writing Center. The Writing Center at UNC-Chapel Hill, 2014. writingcenter.unc.edu. Accessed 1 March 2017.