Loyola University Chicago

Writing Center

When to Use a Comma

The comma has a wide variety of uses, but one of the most common of these is to separate items in a list:

  • “I invited Stan, Phil, and Henry to dinner.”

At some point in your academic career, you might encounter some controversy surrounding the use of the “Oxford comma.” The Oxford comma (also called the serial comma) is placed before the conjunction at the end of a list. The main argument in favor of the comma involves clarity; there are situations in which a missing comma at the end of a list can skew the meaning of the sentence.

Here’s a famous example:

  • “I dedicate this book to my parents, Ayn Rand and God.”

Leaving out the Oxford comma is not technically wrong. It’s important, however, to be conscious of which style you’re using and why.

Comma Splices

A comma splice is a common error. It occurs when a comma is used to join two independent clauses but there isn’t a conjunction following the comma:

  • “I finished my paper on Paradise Lost at 1:00am yesterday morning, I watched TV until 2:00am.”

There are three easy ways the fix this comma splice:

  1. Change the comma to a semi-colon,
  2. Change the comma to a period and turn the independent clauses into separate sentences, or
  3. Keep the comma, but add a conjunction after it to link the clauses.

Independent Clauses

An independent clause is a series of words containing a subject and a predicate, meaning that it can be a stand-alone sentence. If you add a dependent clause to an independent clause, it should be set off with a comma:

  • “I’ll go to the doctor eventually, but only if I start feeling worse.”

If you begin a sentence with an introductory or prepositional phrase, it should be set off from the independent clause with a comma:

  • “Unfortunately, the article’s provocative claims are undermined by the dubious methods of the author.”
  • “On the top shelf of the cupboard, you will find an extra set of silverware.”


Parentheticals are generally descriptors embedded in a sentence that modify, identify, or provide new information about a noun. They are enclosed by commas and can be removed from the sentence without rendering it grammatically incorrect. Parentheticals can come at the beginning or end of a sentence:

  • The Sun Also Rises, which I read over winter break, is one of Ernest Hemingway’s most famous novels.”
  • “The tsetse fly, which is found throughout much of Sub-Saharan Africa, is the primary vector for the disease trypanosomiasis, more commonly known as sleeping sickness.”


Appositives are a form of parenthetical and need to be enclosed by commas. An appositive is a noun or a short descriptive phrase that identifies a noun preceding it.

  • “Part II of The Sound and the Fury is narrated by Caddy’s oldest brother, Quentin, whose fragmented narrative is exemplary of Faulkner’s innovative modernist aesthetic.”
  • “Edmund Burke, one of the major critics of the French Revolution, was an important eighteenth century political theorist and philosopher.”

Coordinate Adjectives

Coordinate adjectives don’t need to be listed in a certain sequence and should be separated by commas.

  • “I found the reading for today’s class to be dry, dense, and unrewarding.”
  • “I rode my bike up the hill to the bright yellow house.” (Note: Adjectives that need to be listed in a certain order do not require a comma.)


This page describes some of the most common uses of the comma, but it is not exhaustive. Consult the resources below for more help.