Jenny Morse, PhD
Author and CEO

If you’re anything like most people, you might not have the good feelings about the color red. Red is the color of blood; it says “pay attention…danger!” It also was *most likely the color your English teachers used to mark up your papers. In my experience, papers quickly turn red from comma splices and run-on sentences.

Remember those circled unnecessary commas (comma splice) or margin comments that said “wordy” or “run-on sentence”? As a professor, I am constantly circling unnecessary commas and correcting run-on sentences.

You might be thinking, do commas or run-on sentences really matter that much? Or, I learned about commas back in grade school, but I don’t remember any of the rules. Don’t I just a throw a comma in before “and” or anytime I pause to take a breath?

The short answers: comma splices and run-on sentences do matter. Not only are they correctness issues, but they help with clarity, so you can clearly articulate what you want to say to your audiences. And, both correctness and clarity establish credibility with your audience.

And, there are pretty straightforward rules for when you should use commas in your sentences (not just when you see “and” or take a breath). Basically, the reason that commas exist is to help us sort the pieces of a sentence. We use commas

Want a more in-depth refresher on professional writing?

Try our Better Business Writing: On Demand course. This self-paced, virtual course will teach you strategies to become a more efficient and effective writer, and provide you with expert feedback

Learn More

1) in lists:

I am going to the store to buy milk, cookies, and bananas.

2) to separate independent (main) and dependent (supporting) clauses (ideas):

When I go to the store, I buy milk.

dependent (supporting) independent (main)

3) and to connect independent clauses (main ideas) connected by a conjunction (and, or but, etc.):

I went to the store to buy milk, and I bought some cookies.

independent (main) independent (main)

“When I go to the store” in #2 is a dependent clause; it depends on something else (I buy milk) to be complete and make sense. Think, if you went up to someone and said “When I go to the store” and stopped there, they would maybe think you’re crazy, and they would say “Yes, go on…”

An independent clause is complete in and of itself. You can add other information to that sentence (which is where commas come in), but you could just say “I buy milk” and people will understand you. This is where comma splices come in.

A comma splice is an error. It is an unnecessary comma that separates two independent clauses. But, a comma can’t do that by itself. So, the comma should be something else: period, semicolon, or comma with a conjunction. Comma splices are a type of run-on sentence, and run-on sentences usually are misusing or just plain missing punctuation that makes them less clear to your reader.

For example:

Mary went to the store to buy milk, she always shops at King Soopers for her groceries.

This sentence is technically two independent clauses or complete sentences. You could say the words on either side of the comma without needing the rest.

Instead, you can write:

Mary went to the store to buy milk. She always shops at King Soopers for her groceries.

Mary went to the store to buy milk; she always shops at King Soopers for her groceries.

Mary went to the store to buy milk, and she always shops at King Soopers for her groceries.

It doesn’t matter which punctuation you use instead of a comma by itself; each of these sentences are correct, so really it depends on your preference. The only thing I suggest is that if you’re in doubt about whether you’re using a semicolon correctly (read about semicolons here), stick with a period.

How can you tell if you used a comma splice?

Ask yourself the following question:

Do the words on both sides of the comma make up complete thoughts? Or, could you go up to someone and say the portions that come before and after the comma as separate sentences, and they make sense?

If so, you have a comma splice, and you can fix it by changing the comma to a period, changing the comma to a semicolon, or adding a conjunction (remember FANBOYS?) to that comma.

Still feeling a bit confused about when to use commas in your writing and how to avoid errors like comma splices and other kinds of run-on sentences? We offer several online courses that could help you brush-up on your grammar and writing to help you become a more efficient and effective writer.

Featured