When you read a run-on sentence out loud, it may sound completely natural, and that's the issue. Take this one:
I finished the essay at midnight, I was too tired to check it.
Chances are you've written one just like it. The message is easily understood and the flow is natural. Nothing looks broken. It'll still be marked by a teacher, an editor or a picky manager, because two complete sentences are dangling on a single comma that can't hold them.
The good news is that run-ons are easy to recognize and follow a predictable pattern. After you pick up the pattern, you'll spot them everywhere, even in your own writing. This guide explains what a run-on sentence is, the two types you'll come across, and four tried-and-true ways to fix them. Then you'll find 31 examples with corrections and a brief quiz to check your work.
What Is a Run-On Sentence?
A run-on sentence is two or more complete sentences connected together without the punctuation or linking word they require. The Purdue Online Writing Lab describes run-ons and comma splices as "names given to compound sentences that are not punctuated correctly."
To understand run-ons, you first need to know what an independent clause is. It's a group of words that has its own subject and verb and can stand on its own as a sentence. Here's one: The bus was late. Here's another: I missed my class. You could end either one with a period and it'd be fine.
The issue arises when two of them are pushed together without the proper connection. The writing tutorial at Northern Illinois University looks at it from another angle: each clause is complete, but the link between them is either missing or the wrong kind.
So the run-on sentence definition isn't based on the length of the sentence. It's about the way its parts are joined together.
The Two Types of Run-On Sentences
Grammar guides don't all have the same names, which doesn't help. Most of them, though, agree on two types.
Fused Sentences
The most obvious form of run-on is the fused sentence. Two clauses collide without any punctuation:
The bus was late I missed my class.
You can usually hear this one. Read it aloud and you'll most likely run out of breath, or trip where the period should be. The stumble is a good indicator.
What Is a Comma Splice?
A comma splice is more difficult to spot. It adds a comma between the two clauses, and the comma seems to be doing its job. It isn't. Here's how the Purdue OWL guide to clauses puts it: "A comma splice is the use of a comma between two independent clauses."
The bus was late, I missed my class.
The comma splice meaning in a dictionary is almost the same. Merriam-Webster gives essentially the same definition, and it dates the first known use of the term to 1924.
Is a comma splice a run-on sentence? Usually, yes. Think of "run-on" as the family name. Fused sentences and comma splices are the two members of the family.
A Long Sentence Is Not Always a Run-On
This is the myth that we most want to dispel. Many people think a run-on sentence is a sentence that is too long. It isn't.
This is a grammatically correct long sentence:
When the storm finally passed and the power came back on just after midnight, the people on our floor, who had spent the whole evening sharing candles and snacks in the hallway, slowly drifted back to their own apartments.
There are 39 words and only one independent clause: the people on our floor slowly drifted back. All the rest is built on this foundation. Now compare it with this:
It's late, I'm going home.
Only five words, and it's a comma splice. It's simply stated in the course notes on Lumen Learning: "Length is no guarantee of a run-on sentence."
The Grossmont College grammar guide says the same thing, cautioning readers against assessing a sentence by its length.
Of course, long sentences can be difficult to read. This is a style issue, not a grammar issue, and we address this further on.
How to Fix a Run-On Sentence or Comma Splice: 4 Ways
There is not necessarily one right solution. The decision will be based on the relationship between the two ideas and the rhythm you want. The following four repairs build on the four standard repairs listed in the Northern Illinois University guide, and are presented in the order we find most useful.
For all four, we'll be using one broken sentence, so you can see how each fix affects the feel:
The bus was late, I missed my class.
Fix 1: Split It Into Two Sentences
The simplest repair is to put a period (a full stop) where the comma is and start a new sentence.
The bus was late. I missed my class.
This is almost always effective, and it's the safest option when you're not sure. It also lends some emphasis to each idea, which can be useful when you want your reader to stop and think. The only danger is overuse: a paragraph that is a string of short sentences can start to feel like a list of facts.
The fix: use this for sentences that were becoming too crowded, or when the two ideas are fairly distinct. If a sentence has become too long to untangle by eye, a free sentence shortener can show you a shorter version to begin with.
Fix 2: Join the Two Clauses
If the ideas go together, keep them in a single sentence and link them correctly. This is typically the solution when you're not sure how to fix a comma splice without altering your meaning. There are two choices available.
The first is a comma plus a coordinating conjunction. There are only seven of them, commonly referred to as FANBOYS: for, and, nor, but, or, yet, so.
The bus was late, so I missed my class.
The second is a semicolon, which may be used to join two closely related clauses that are not connected by a conjunction.
The bus was late; I missed my class.
There's one thing to be aware of here. Words like however, therefore and as a result feel like joining words, but they cannot join two clauses with only a comma. The Lumen Learning chapter explains that they need a semicolon before them. Starting a new sentence works too.
Wrong: The bus was late, however, I made it to class.
Right: The bus was late; however, I made it to class.
The fix: if you want to indicate the link (cause, contrast, choice), use a comma followed by a FANBOYS word. If the connection is clear and you want a tighter rhythm, use a semicolon.
Fix 3: Make One Clause Depend on the Other
One of the clauses may be made a dependent clause as well. That means using a conjunction such as because, although, when, while, since, if or after to make part of the sentence dependent.
I missed my class because the bus was late.
Because the bus was late, I missed my class.
Pay attention to the comma rule. If the dependent part is first, place a comma at the end of it. If it is second, you typically don't need one.
This fix tends to read best, since it illustrates exactly how the two ideas are related. The result is known as a complex sentence, and our guide to complex sentences covers it in more detail.
The fix: use this when one idea leads to, explains or contrasts with the other.
Fix 4: Rewrite the Sentence
In certain cases, the best repair is to stop patching and express it in other words. This is effective when the clauses repeat each other or when the sentence is not very well formed.
The late bus made me miss my class.
It is shorter and more succinct, and has only one clause remaining.
The fix: apply this when the other three fixes all sound awkward. If you're struggling with the wording, a sentence rewriter can offer you a couple of options. Pick the one that still sounds like you.
How to Fix a Very Long Run-On
Not all run-ons are two clauses connected together. Some are four or five, linked together by commas and the word then. They are often found in rushed emails and initial drafts.
Separating each clause into a sentence corrects the grammar, but it may sound choppy. Instead, it is better to identify the main idea, state it in a single sentence, and then organize the supporting details around the main idea. Typically you will use Fix 1 in conjunction with Fix 2 or Fix 3.
If you don't see where to begin, sometimes it's easier to first view a cleaner version. Paste the sentence into our tool to simplify sentences, then compare its version with yours and keep what works.
31 Run-On Sentence Examples and Comma Splice Examples (With Corrections)
Each example shows the broken sentence, a corrected version and the fix it uses. The second group covers comma splice examples and corrections. Most have more than one correct answer, so if your version is different but follows one of the four fixes, it is probably fine.
Fused Sentences
1. My phone died I could not call you. Corrected: My phone died, so I could not call you. (Fix 2)
2. The meeting starts at nine bring your laptop. Corrected: The meeting starts at nine. Bring your laptop. (Fix 1)
3. She loves hiking her brother hates it. Corrected: She loves hiking, but her brother hates it. (Fix 2)
4. The cake is in the oven don't open the door. Corrected: The cake is in the oven, so don't open the door. (Fix 2)
5. It rained all weekend we stayed in and watched films. Corrected: Because it rained all weekend, we stayed in and watched films. (Fix 3)
6. I have read the report it raises some good points. Corrected: I have read the report; it raises some good points. (Fix 2)
7. The bus was late I missed the first class. Corrected: I missed the first class because the bus was late. (Fix 3)
8. Our dog barks at every delivery driver he is friendly once they come inside. Corrected: Our dog barks at every delivery driver, but he is friendly once they come inside. (Fix 2)
9. Tickets go on sale Friday they usually sell out within an hour. Corrected: Tickets go on sale Friday. They usually sell out within an hour. (Fix 1)
10. The app keeps crashing nobody knows why. Corrected: The app keeps crashing, and nobody knows why. (Fix 2)
Comma Splices
11. I finished the essay at midnight, I was too tired to check it. Corrected: I finished the essay at midnight, but I was too tired to check it. (Fix 2)
12. The coffee was cold, the service was slow. Corrected: The coffee was cold, and the service was slow. (Fix 2)
13. Sam isn't coming tonight, he has a cold. Corrected: Sam isn't coming tonight because he has a cold. (Fix 3)
14. Please reply by Monday, we need the numbers for the report. Corrected: Please reply by Monday. We need the numbers for the report. (Fix 1)
15. The film was long, I enjoyed every minute. Corrected: Although the film was long, I enjoyed every minute. (Fix 3)
16. My sister lives in Toronto, she moved there last year. Corrected: My sister has lived in Toronto since last year. (Fix 4)
17. The printer is out of ink, someone needs to order more. Corrected: The printer is out of ink, so someone needs to order more. (Fix 2)
18. I called twice, nobody answered. Corrected: I called twice, but nobody answered. (Fix 2)
19. Water the plants on Tuesday, they dry out fast in summer. Corrected: Water the plants on Tuesday. They dry out fast in summer. (Fix 1)
20. The test was easier than I expected, I still checked every answer twice. Corrected: Even though the test was easier than I expected, I still checked every answer twice. (Fix 3)
21. He said sorry, it was too late. Corrected: He said sorry, but it was too late. (Fix 2)
22. Our team won the first game, we lost the next three. Corrected: Our team won the first game; we lost the next three. (Fix 2)
Comma Splices With However, Therefore and Similar Words
23. I wanted to come, however, I had to work late. Corrected: I wanted to come; however, I had to work late. (Fix 2)
24. The road was closed, therefore, we took the long way round. Corrected: The road was closed; therefore, we took the long way round. (Fix 2)
25. Prices went up again, as a result, we dropped the subscription. Corrected: Prices went up again. As a result, we dropped the subscription. (Fix 1)
26. The instructions were clear, then I lost them. Corrected: The instructions were clear, but then I lost them. (Fix 2)
27. She trained every day, consequently, she ran her fastest race yet. Corrected: She trained every day. Consequently, she ran her fastest race yet. (Fix 1)
Long Run-On Sentences
28. We got to the airport early, the flight was delayed, then the gate changed twice, by the time we boarded everyone was exhausted. Corrected: We got to the airport early, but the flight was delayed and the gate changed twice. By the time we boarded, everyone was exhausted. (Fixes 1 and 2)
29. I opened the laptop to answer one email I ended up reading the news for an hour then I forgot what the email was about. Corrected: I opened the laptop to answer one email. An hour of news later, I had forgotten what the email was even about. (Fixes 1 and 4)
30. The landlord said he would fix the heater, that was three weeks ago, it is still broken, we have been using blankets. Corrected: The landlord promised to fix the heater three weeks ago. It is still broken, so we have been living under blankets. (Fixes 1, 2 and 4)
31. The recipe looked simple, it only had five ingredients, I didn't have two of them, so I improvised, it did not go well. Corrected: The recipe looked simple, with only five ingredients. I didn't have two of them, so I improvised. It did not go well. (Fixes 1 and 4)
Is This a Run-On Sentence? How to Spot One in Your Own Writing
It's easy to identify run-ons in other people's writing. It will be much more difficult to see them in your own, since you know what you intended. Your brain fills in the missing punctuation for you.
For fused sentences, reading aloud will help you find the place where the period should go. Comma splices are not the same. They typically sound okay when spoken out loud, which is why they get through. For them, a slower check is better suited.
Step 1: Find every subject and verb. Read a sentence and circle who is doing what. The bus (subject) was (verb). I (subject) missed (verb).
Step 2: Count the independent clauses. Do you think each subject/verb combination could be a sentence? If you find 2 or more, proceed to step 3.
Step 3: Check what joins them. Two independent clauses require a period, a semicolon, a comma and a FANBOYS word, or a word such as because that makes one dependent on the other. A single comma is not sufficient, and neither is leaving the gap empty.
Certain words, such as then, also, however, therefore, plus and as a result, should grab your attention when they follow a comma. They frequently end up where one sentence ought to end and the next ought to start. One of the easiest ways to avoid run-on sentences is to learn to pause on these words.
When a whole paragraph seems like one big breath, reword the paragraph as a block instead of sentence by sentence. A paragraph rewriter can provide you with a new version to compare with your version, making the weak joins more apparent.
When a Comma Splice Is Allowed
This is the part that people don't expect. Not all comma splices are errors. They are used on purpose by good writers, particularly in fiction and informal writing.
The editors behind the Chicago Manual of Style cover this on CMOS Shop Talk. Their view is that "a comma splice can work well, especially if the tone is informal." It helps most if the clauses are short and have a consistent structure. Their examples include the well-known beginning of Charles Dickens's A Tale of Two Cities: It was the best of times, it was the worst of times. They also reference a line from Virginia Woolf's To the Lighthouse and from José Saramago's Blindness, in which the author uses comma splices as a deliberate style throughout the novel.
You can see how it's effective in a short line such as I came, I saw, I conquered. If you were to break it up into three sentences, you'd lose the momentum.
That said, the rule of thumb is simple. In school essays, job applications, work reports and anything formal, treat comma splices as errors. There, a comma splice can make careful writing look careless. Reserve the deliberate ones for creative work, where the effect is meant.
Run-On Sentence Practice: 10 Questions With Answers
These run-on sentence examples and answers let you test yourself. Try each one before you look at the answers. Some contain a run-on sentence and some do not. Three of them are already correct, so read carefully.
1. The kettle clicked off, I poured the tea.
2. Although the shop was closed, the lights were still on.
3. We missed the train we had to wait an hour.
4. I like the blue one the red one is cheaper.
5. The email bounced back, the address must be wrong.
6. My brother, who lives two streets away and visits every Sunday with his kids, his dog and a box of pastries, finally learned to knock.
7. It is late, however, the shop is still open.
8. Turn left at the church the café is on your right.
9. She smiled, waved and walked away.
10. The update fixed the bug, it also made the app slower.
Show the answersHide the answers
- Comma splice. One fix: The kettle clicked off, and I poured the tea.
- Correct. The first part cannot stand alone, so the comma is fine.
- Fused sentence. One fix: We missed the train, so we had to wait an hour.
- Fused sentence. One fix: I like the blue one, but the red one is cheaper.
- Comma splice. One fix: The email bounced back; the address must be wrong.
- Correct. It is long, but there is only one independent clause: My brother finally learned to knock.
- Comma splice. One fix: It is late; however, the shop is still open.
- Fused sentence. One fix: Turn left at the church. The café is on your right.
- Correct. There is one subject, she, doing three things, so there is only one clause.
- Comma splice. One fix: The update fixed the bug, but it also made the app slower.
If you got eight or more right, you have the pattern. If question 6 or 9 caught you out, go back to the three-step check above. Both are built to look like run-ons when they are not.
Frequently Asked Questions
Are Run-On Sentences Grammatically Incorrect?
Yes. A run-on sentence is a grammar problem in standard written English in which the clauses are not properly connected. The one exception is a deliberate comma splice in creative or informal writing.
Is a Comma Splice a Run-On Sentence?
Yes, in most grammar guides. A comma splice is one of the two types of run-on sentence. The other is a fused sentence: a sentence that lacks any punctuation between clauses.
Can a Short Sentence Be a Run-On?
Yes. It's late, I'm going home is only five words long, but it is a comma splice. Whether a sentence is a run-on depends on how its clauses are joined, not on how many words it has.
Does However Need a Semicolon?
Yes, if however connects two independent clauses. Use a semicolon before it and a comma after it, or start a new sentence. However, when it is used in one clause, as in The plan, however, failed, commas will suffice.
How to Avoid Run-On Sentences
Look in every sentence for more than one subject/verb combination that could be a sentence. When you find two, make sure they are joined by a period, a semicolon, a comma with and, but, or, so, for, nor or yet, or a word like because or although.
The Bottom Line
Run-ons have nothing to do with length, and they have nothing to do with sounding wrong. It all boils down to one question: is there something strong enough connecting the two complete thoughts? A single comma will not do the job. A period, a semicolon, a comma followed by a FANBOYS word, or a dependent clause always does.
As soon as you begin to search for that one join, you'll see most run-ons in seconds. If it's a more difficult case, the free tools on TotBot can assist. The sentence shortener is used to shorten a sentence that has become too long. The sentence rewriter can give you a new way to say it, and our sentence simplifier can do the really tangled ones. If you want to look at an entire text again, use the paragraph rewriter.
Quick Reference: 4 Ways to Fix a Run-On Sentence
| Fix | How it works | Example | Best for |
|---|---|---|---|
| Split It Into Two Sentences | Replace the comma with a period | The bus was late. I missed my class. | Separate ideas or crowded sentences |
| Join the Two Clauses | Add a comma and a FANBOYS word, or use a semicolon | The bus was late, so I missed my class. | Closely linked ideas |
| Make One Clause Depend on the Other | Add a word like because, although or when | I missed my class because the bus was late. | Cause, reason or contrast |
| Rewrite the Sentence | Say it a different way | The late bus made me miss my class. | Awkward or repetitive sentences |
Sources: Purdue OWL: Run-ons and Comma Splices; Purdue OWL: Independent and Dependent Clauses; Merriam-Webster: Comma splice; Northern Illinois University: Run-on Sentences; Grossmont College: Run-on Sentences; Lumen Learning: Run-on Sentences; CMOS Shop Talk: Comma Splices and Run-On Sentences.