What Are Run-on Sentences? Explained

Wondering what are run-on sentences? This guide will explain this common error and how to fix it.

If you are going to be a skilled writer, you must know the answer to an important grammar question: what are run-on sentences? The run-on is one of the most basic grammar mistakes, and it’s an easy one to fall into if you are not careful. 

This guide will help you avoid merging two complete sentences incorrectly and creating a run-on. It will also explore examples of this common error, so you can learn to spot, and avoid, it in your own writing.

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what are run-on sentences? Examples and Grammar Rules for Compound Sentence Construction

What are run-on sentences?

A run-on sentence is also known as a comma splice or fused sentence. It is a sentence made from more than one independent clause joined incorrectly.

In the English language, it is possible to join two independent clauses. However, you need to do so with the proper punctuation and conjunctions in place to avoid creating a run-on. Learning how to avoid run-on sentences is a key part of writing well. You might also find our guide on filler sentences helpful.

Spotting a Run-On

A complete sentence has a subject and a verb and states a complete thought. To spot a run-on, you need to look for a long sentence with two or more complete sentences. Here is an example: 

  • I love to eat ice cream I could eat it every day.

This sentence is a run-on because it has two sentences merged together into one. You could re-write this in a couple of ways:

  • I love to eat ice cream. I could eat it every day.
  • I love to eat ice cream, and I could eat it every day.
  • I love to eat ice cream; I could eat it every day.

Joining the sentences using a comma and conjunction or a semicolon makes it a compound sentence. Separating the two clauses into two separate sentences is also correct.

Type of Run-On: Comma Splice 

A comma splice is a prevalent type of run-on. It happens when you join two separate independent clauses with just a comma. Here is an example of a comma splice:

  • The students could turn their papers in at any time, I chose to turn mine in early.

This is actually two sentences:

  • The students could turn their papers in at any time.
  • I chose to turn mine in early

Joining them with just a comma is not sufficient.

Type of Run-On: Fused Sentence

A fused sentence combines two simple sentences with no connecting word or with a transitional expression that is not a conjunction. For example:

  • The study did not have the desired result therefore the researchers did another round.

Though this has a transitional word, therefore is not a conjunction, and as such, it is a fused sentence. 

Fixing Run-On Sentences

What are run-on sentences?
Adding a semicolon can fix run-on sentences

There are four ways to fix run-on sentences. They are:

  • Adding a comma and coordinating conjunction
  • Adding a subordinating conjunction
  • Adding a semicolon
  • Separating the two sentences 

1. Comma and Coordinating Conjunction

One of the simplest ways to fix a run-on sentence is to add a comma and a coordinating conjunction between the two simple sentences. Here is an example run-on sentence: 

  • The students could turn their papers in at any time I chose to turn mine in early.

This is a run-on because it has two separate sentences combined without any punctuation marks or conjunctions. Instead, you could say:

  • The students could turn their papers in at any time, but I chose to turn mine in early.

2. Subordinating Conjunction

You can also use a subordinating conjunction to fix a run-on, in which case you do not need the comma. Sometimes to keep the meaning, you will need to rearrange sentence structure. Using the previous example, here is how a subordinating conjunction might look:

  • I chose to turn my paper in early though the students could turn them in at any time.

3. Semicolon

Another way to fix a run-on is to use a semicolon between the two sentences. This eliminates the need for a conjunction. It shows that the two sentences are connected, but separate, sentences.

For example:

  • The students could turn their papers in at any time; I chose to turn mine in early.

4. Separating the Sentences

The final way to fix run-ons is to simply separate the two sentences. You could write:

  • The students could turn their papers in at any time. I chose to turn mine in early.

A Word of Warning: Dependent Clauses

When you are writing complex sentences, such as in academic writing, you will likely use a number of dependent clauses. Because these sentences can get long, they may look like run-ons, but in fact, are not. For example:

  • While running away from the police, the thieves made a blunder and gave their position away.

This sentence has a dependent clause, “while running away from the police,” followed by a complete independent clause, “the thieves made a blunder and gave their position away.” It is correct the way it stands and does not need any additional punctuation or conjunctions. 

If you are evaluating a piece of writing looking for run-on sentences, always watch out for dependent clauses. If a clause does not have a subject and a verb, it is dependent, and the run-on rules do not apply.

A Final Word on What Are Run-on Sentences

Run-on sentences are sentences that combine two or more dependent clauses without the right punctuation and conjunctions. This error is easy to make in your English writing.

As you learn to be a better writer, use caution to watch for fused sentences and comma splices. Studying examples of run-on sentences will help you get better at avoiding them in your writing.

Need help with fixing run-on sentences? A good grammar checker is ideal. It’ll help you find and fix odd capitalization issues fast.

To find out more, read our Grammarly review


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FAQs on What Are Run-on Sentences

What are run-on sentences?

Run-on sentences are sentences that improperly join two or more complete sentences. To join sentences, you need a comma and conjunction, subordinating conjunction or semicolon. Otherwise, you have a run-on. 

Can a run-on sentence have a comma?

Yes, a sentence that has a comma can still be a run-on. For example:
The privacy notice was unclear, it did not explain third-party information sales.
This should read:
The privacy notice was unclear, for it did not explain third-party information sales.
The privacy notice was unclear because it did not explain third-party information sales.


  • Nicole Harms has been writing professionally since 2006. She specializes in education content and real estate writing but enjoys a wide gamut of topics. Her goal is to connect with the reader in an engaging, but informative way. Her work has been featured on USA Today, and she ghostwrites for many high-profile companies. As a former teacher, she is passionate about both research and grammar, giving her clients the quality they demand in today's online marketing world.