Run-Ons and Comma Splices
Run-ons and comma splices are one of the most common grammatical errors in student writing.
Run-ons are two sentences that are stuck together without a linking word. For example:
| Fabio loves cats he loves dogs even more. |
| Cheese is Sarah's favorite food she eats it every day. |
The most common kind of run-on is a comma splice, which is two sentences linked together with a comma:
| Fabio loves cats, he loves dogs even more. |
| Fred is not crazy, he is just creative. |
Recognizing Run-Ons and Comma Splices
Sometimes it can be difficult to identify run-ons and comma splices in your own writing. Many people believe that any long sentence is a run-on, but this is not the case. It is possible to have very long sentences that are not run-ons and very short sentences that are run-ons. For example:
| run-on | Bill loves me I love him, too. |
| not a run-on | Although Bill loves me and I love him, I worry that perhaps our love will not be enough to sustain us through today's difficult world, in which so many previously happy couples are driven to deception, infidelity, and ultimately divorce. |
While the second sentence is long and confusing, it is not grammatically incorrect. Every part of the sentence has been linked properly, and there is no place that the sentence could be split into two halves that could both stand alone as sentences. On the other hand, the first sentence can be split into two halves that could each stand alone as a sentence:
| sentence one | sentence two |
| Bill loves me. | I love him, too. |
When trying to determine if a sentence is a run-on, a comma splice, or a correct sentence, consider the following questions:
1. Could the sentence be split into two halves that could each stand alone as a sentence?
- If yes, then it is a run-on.
- If no, then it is not a run-on.
2. Is there a comma in the sentence? If so, could the material on each side of the comma stand alone as a complete sentence?
- If yes, then it is a comma splice.
- If no, then it is not a comma splice.
Fixing Run-Ons and Comma Splices
There are three main ways to fix run-ons and comma splices:
- Add a period.
- Add a semicolon.
- Add a conjunction (linking word).
Add a Period
The simplest way to fix a run-on or comma splice is by dividing it into two separate sentences.
| run-on or comma splice | corrected sentence(s) |
| Cheese is Sarah's favorite food, she eats it every day. | Cheese is Sarah's favorite food. She eats it every day. |
| Rachel doesn't like to eat cheese, she is lactose intolerant. | Rachel doesn't like to eat cheese. She is lactose intolerant. |
Add a Semicolon
You may find that sometimes you would like to connect two sentences together because their ideas are closely connected. One way you can do this is with a semicolon, which looks like a comma with a dot on top of it. A semicolon links two complete sentences, so it is a perfect way to correct a run-on or comma splice.
| run-on or comma splice | corrected sentence(s) |
| Cheese is Sarah's favorite food, she eats it every day. | Cheese is Sarah's favorite food; she eats it every day. |
| Fred is not crazy, he is just creative. | Fred is not crazy; he is just creative. |
Mistakes with Semicolons
There are a couple of common mistakes to watch out for when using semicolons.
- Semicolons are considered special punctuation and should not be used too often. Try to limit yourself to one semicolon per paragraph unless you have a good reason to use more.
- Semicolons should only be used to connect two complete sentences. Be careful not to use a semicolon to connect a partial sentence. Instead, use either a comma or no punctuation at all, depending on the structure of the sentence.
| Incorrect Semicolon Use | Corrected Sentence |
| Bill loves crackers; because they are crispy. | Bill loves crackers because they are crispy. |
| Knowing that she was late for work; Kate snuck in the back door. | Knowing that she was late for work, Kate snuck in the back door. |
| Juan loves movies including; Juno and No Country for Old Men. | Juan loves movies including Juno and No Country for Old Men. |
Add a Conjunction
A third way to fix a run-on or comma splice is by adding a conjunction, or linking word, to link the two complete setences together. Find out more about conjunctions.
Coordinating Conjunctions
Coordinating conjunctions like "and" or "but" must go between the two halves of the sentence. Coordinating conjunctions must be proceeded by a comma when they are linking two complete setnences.
| run-on or comma splice | corrected sentence(s) |
| Fabio loves cats he loves dogs even more. | Fabio loves cats, but he loves dogs even more. |
| Cheese is Sarah's favorite food, she eats it every day. | Cheese is Sarah's favorite food, and she eats it every day. |
To learn more about how to use coordinating conjunctions, see the Coordination/Subordination page.
Subordinating Conjunctions
Subordinating conjunctions like "because" and "although" can be attached to either the first or second half of the sentence. If they are attached to the first half of the sentence, you must include a comma before the second half of the sentence to show where it splits.
| run-on or comma splice | corrected sentence(s) |
| Fabio loves cats he loves dogs even more. | Although Fabio loves cats, he loves dogs even more. |
| Boris forgot to bring his wallet, he had to run home and get it. | Because Boris forgot to bring his wallet, he had to run home and get it. |
Camilla got sick she had to stay home from work. |
When Camilla got sick, she had to stay home from work. |
If the subordinating conjunction is attached to the second half of the sentence, no comma is needed in most cases.
| run-on or comma splice | corrected sentence(s) |
| Lucille is friendly she is shy at first. | Lucille is friendly although she is shy at first. |
| Rachel doesn't like to eat cheese, she is lactose intolerant. | Rachel doesn't like to eat cheese because she is lactose intolerant. |
| Lisa used the hammer she found it in the drawer. | Lisa used the hammer that she found in the drawer. |
To learn more about how to use subordinating conjunctions, see the Coordination/Subordination page
This page was created by Karin Spirn.
