We’ve covered when not to use commas (and when to use commas if you feel like it), but it’s just as important to know when to use commas. We can’t have run-on sentences taking over literature. So when do you use a comma?

When Should You Use a Comma

Photo by JD Hancock

We’ve already covered the Oxford comma and the need for commas in a series or list. There are three other primary times when you need to use a comma. Keep in mind that this is not an exhaustive list; just the times when comma use is most common.

You Should Use a Comma…

1. When connecting two sentences with a coordinating conjunction.

James loves his dog. His dog loves eating weird things. To combine those sentences, use a comma with a conjunction. James loves his dog, and his dog loves eating weird things.

2. When adding words or phrases to the beginning or end of your main sentence.

Joan dreams of becoming a professional bodybuilder. If we wanted to modify that sentence with a word or phrase before or after it, we’d add a comma between the modifier and the main sentence. Oddly, Joan dreams of becoming a professional bodybuilder. Joan dreams of becoming a professional bodybuilder, even though her mother would prefer she become a dental hygienist.

3. On both sides of a nonessential part of the sentence.

Any time you add extra details to a sentence that are not necessary for comprehension, add commas on either side of that extra phrase. Jessica, whose sister had trained her to scream at the sight of blood,  shrieked at the top of her lungs when she saw Jake’s ketchup-covered arm. The sentence is still completely understandable without the clause enclosed in commas (Jessica shrieked at the top of her lungs when she saw Jake’s ketchup-covered arm.). The clause just adds extra context, and since it is not essential, you would surround it with commas.


Take fifteen minutes and write about a competitive scenario: a state championship soccer game, a Super Bowl, a sixth-grade spelling bee. Use commas appropriately when describing what’s going through the players’/spectators’/anxious parents’ heads, and when describing the action that’s taking place.

Post your practice in the comments, and leave notes for your fellow practicers.

Liz Bureman has a more-than-healthy interest in proper grammatical structure, accurate spelling, and the underappreciated semicolon. When she's not diagramming sentences and reading blogs about how terribly written the Twilight series is, she edits for the Write Practice, causes trouble in Denver, and plays guitar very slowly and poorly. You can follow her on Twitter (@epbure), where she tweets more about music of the mid-90s than writing.

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