Commas: Three Simple Rules

July 22, 2025

Posted by STLCC in Tutoring Resources 

Comma Usage

To master comma rules, the first step is to figure out why a comma is being used. A comma is a punctuation mark that indicates a pause in the sentence. The most common three rules of commas involve introducers, interrupters, and add-ons.

Sometimes even an instructor’s marks on an essay don’t help. If you’ve used too many commas this time, on the next paper you might not use any--and vice versa. Many of those 60-odd comma rules boil down to this:

Commas are used most frequently for: introducers, interrupters, and add-ons.

Check your own writing for these three uses, and you’ll begin to master commas.

Introducers

An introducer is a word, phrase, or clause that comes before an independent clause in a sentence (example introducers are in bold).

• Well, I guess it’s time to start my English paper.
• Because it’s 3 a.m. Monday, I should start my English paper.
• Most of the time, I start my English paper the morning it’s due.

Interrupters

An interrupter is a word, phrase, or clause that comes in the middle of an independent clause in a sentence (example interrupters are in bold).

• My composition instructor, knowing my habit of procrastinating, reminded me to start early on my essay.
• Most student writers, even good ones who get decent grades on their essays, feel unsure about their ability.
• Good writing, I believe, happens because the writer has something important to share with the reader.

Add-Ons

An add-on is a word, phrase, or clause that comes at the end of an independent clause in a sentence (example add-ons are in bold).

• Students whose essays are late blame lack of time, no matter what excuses they’ve used before.
• It’s hard for me to write an introductory paragraph, which slows down my writing process.
• I’ve never enjoyed writing, to tell you the truth.

Learn more about comma rules.