Using Commas
Commas are used to separate one idea from another in a sentence. They help your reader differentiate between ideas in more complex sentences and follow more complicated trains of thought than can be expressed without commas. This handout explains the different places you can use commas to make your ideas clearer and better organized.
With Clauses
Clauses are phrases that contain a subject and a predicate. They can either stand alone as a sentence (independent clause) or must be attached to another clause to form a complete sentence (dependent clause). Commas are necessary to attach dependent clauses together. See our Clauses handout to learn more.
Use a comma to separate two independent clauses: Independent clauses can be combined in multiple ways, but the most common is to use a coordinating conjunction – for, and, nor, but, or, yet, so. Use a comma before the coordinating conjunction when connecting two independent clauses.
Example: “She ate her lunch, and he went to class.”
Use a comma after an introductory clause or modifier: Dependent clauses are often the first part of a sentence and add information to the independent clause they are attached to. If a sentence begins with a conjunction such as “although”, “after”, or “despite”, use a comma after it. There are also shorter introductory modifiers that usually also start with a conjunction. These are also followed by a comma.
Ex: “Although he was tired, Yijian managed to make it to his early morning class on time.”
Ex: “However, Samira’s alarm didn’t go off and she was late to class.”
Use commas before and after a free modifier: Similar to the above introductory clauses, modifiers interject additional information into a sentence, usually giving more context to a noun. Like clauses, not all modifiers require a comma to be used in a sentence. Free modifiers, which add information without disrupting the flow of a sentence, can be placed at the beginning, middle, or end of a sentence without becoming misplaced or dangling. See our handout Using Modifiers to learn more.
Ex: “The Svalbard Global Seed Vault, containing over one million different varieties of seeds, was created as a safeguard to the world’s future crop supply and diversity.”
With Quotations
When quoting another person or piece of writing, use a comma before the quote when using an introductory phrase such as “say”, “reply”, or “noted”.
Ex: Benjamin Franklin wrote, “Either write something worth reading or do something worth writing.”
Other Cases
Use commas to separate items in a list or series: When describing a list or series of items, use a comma between each item to separate them and indicate to your reader that it is a series being described.
Example: “My favorite fruits are raspberries, apples, and guava.”
The Oxford Comma: There is some debate about whether the last comma in a list or series, which comes before the word “and” or “or”, is necessary. While omitting it may cause ambiguity, refer to the style guide (MLA, APA, etc.) you are writing in to determine whether you need to use it or not.
Example without Oxford comma: “She went to the store with Namrata, her roommate and her coworker.
In this example, it is unclear whether “her roommate and her coworker” are two separate people, or if this is a parenthetical phrase being used to describe Namrata, who is both her roommate and coworker. Fix this by either reorganizing the list or using the Oxford comma, which are both demonstrated below.
Example: “She went to the store with her coworker, her roommate, and Namrata.
Adapted from “Five Comma Rules” by Julie-Francoise Kruidenier ’02
By Laura Widman, Writing Center Assistant Director
Copyright 2024
Nesbitt-Johnston Writing Center, Hamilton College
Hamilton.edu/writing
