What Is a Run-On Sentence? Examples and How to Fix It
A run-on sentence joins two or more independent clauses without the punctuation or connecting word they need. Fix it by splitting it with a period, using a semicolon, adding a comma plus "and", "but" or "so", or turning one clause into a dependent clause with a word like "because" or "although".
Key takeaways
- A run-on sentence joins two independent clauses incorrectly.
- The two main types are fused sentences (no punctuation) and comma splices (only a comma).
- There are four standard fixes: a period, a semicolon, a comma plus a coordinating conjunction, or a subordinating conjunction.
- A long sentence is not automatically a run-on, and a short one can be.
- Words like "however" and "therefore" need a semicolon or period before them, not just a comma.
Table of contents
- What is a run-on sentence?
- What are the types of run-on sentences?
- Fused sentences
- Comma splices
- How do you fix a run-on sentence?
- 1. Split it with a period
- 2. Use a semicolon
- 3. Add a comma and a coordinating conjunction
- 4. Use a subordinating conjunction
- Is a long sentence always a run-on?
- Watch out for "however" and "therefore"
- What's the difference between a run-on and a sentence fragment?
- Practice: spot the run-on
- Quick checklist before you hit submit
A run-on sentence happens when you join two complete sentences without the right punctuation. It's one of the most common grammar mistakes in essays and emails, and it's easy to fix once you can spot it.
Here's what a run-on sentence looks like, the two types you'll come across and four simple ways to correct one.
What is a run-on sentence?
Every complete sentence has at least one independent clause: a subject and a verb that express a full thought. "The bus was late" is an independent clause. So is "I missed my class".
A run-on sentence crams two or more independent clauses together without the punctuation or connecting word they need:
❌ The bus was late I missed my class.
Your reader has to work out where one thought ends and the next begins. In short texts it's a minor annoyance. In an essay it costs marks.
What are the types of run-on sentences?
Purdue OWL groups run-ons, comma splices and fused sentences together as one family of errors. You'll usually meet two versions.
Fused sentences
Two independent clauses with no punctuation at all between them.
❌ My phone died I couldn't call you.
Comma splices
Two independent clauses joined only by a comma. This is the version most people write, because the comma feels like enough of a pause.
❌ My phone died, I couldn't call you.
How do you fix a run-on sentence?
You have four options. Each one is correct; pick the one that fits the meaning you want.
| Fix | Example | Best when |
|---|---|---|
| 1. Use a period | My phone died. I couldn't call you. | Both ideas deserve equal weight |
| 2. Use a semicolon | My phone died; I couldn't call you. | The ideas are closely linked |
| 3. Comma + and, but, or, so | My phone died, so I couldn't call you. | You want to show the relationship |
| 4. Make one clause dependent | Because my phone died, I couldn't call you. | One idea explains the other |
1. Split it with a period
The simplest fix. Two short sentences are often clearer than one long one, and they add punch.
2. Use a semicolon
A semicolon joins two complete thoughts that belong together. Don't overuse it; one or two per page is plenty.
3. Add a comma and a coordinating conjunction
The seven coordinating conjunctions are for, and, nor, but, or, yet and so, often remembered as FANBOYS. Put a comma before the conjunction: "It was raining, but we went anyway."
4. Use a subordinating conjunction
Words like because, although, since, when, while and after turn one clause into a dependent clause, which can't stand alone. "Although it was raining, we went anyway."
Is a long sentence always a run-on?
No, and this is the biggest myth about run-ons. Length has nothing to do with it. This 30-word sentence is perfectly correct:
✅ When the results came in on Friday afternoon, the whole team gathered around Maya's laptop, and nobody said a word until she scrolled to the final number.
Meanwhile, "I came I saw" is only four words, and it's still a run-on sentence. What matters is how the clauses are joined, not how many words there are.
That said, very long sentences are harder to read even when they're correct. If your writing has lots of them, our sentence counter shows your total sentences and words, so you can check your average sentence length.
Watch out for "however" and "therefore"
Words like however, therefore, consequently and otherwise are not conjunctions. They can't join two sentences with just a comma.
❌ I studied all night, however I failed the test.
✅ I studied all night; however, I failed the test.
✅ I studied all night. However, I failed the test.
What's the difference between a run-on and a sentence fragment?
They're opposite problems. A run-on has too much: two complete thoughts squeezed into one sentence. A fragment has too little: it's missing a subject, a verb or a complete thought, so it can't stand on its own.
❌ Fragment: Because the meeting ran late.
✅ Fixed: We missed the train because the meeting ran late.
Ironically, people sometimes fix a run-on and create a fragment by accident. If you split a sentence with a period, check that both halves still have a subject and a verb. Our guide on counting sentences in a paragraph explains how to tell where one complete sentence ends and the next begins.
Practice: spot the run-on
Which of these are run-on sentences? Answers below.
- The meeting ran late, we missed the train.
- We missed the train because the meeting ran late.
- She loves coffee she drinks three cups a day.
- He wanted to come; his car wouldn't start.
Answers: 1 is a comma splice. 2 is correct. 3 is a fused sentence. 4 is correct; the semicolon joins the clauses properly.
Quick checklist before you hit submit
- Find each subject and verb pair. Two pairs usually means two clauses.
- Check what joins them: a period, semicolon, comma plus FANBOYS or a subordinating word.
- A comma alone between two complete thoughts? That's a comma splice.
- Read the sentence aloud. If you naturally stop for breath in the middle, it may need a period.
Clean sentences make your writing easier to follow. Once you can spot a run-on, you'll start catching them in your own drafts before anyone else does. Want to check the length of your paragraphs while you edit? Paste your draft into our paragraph counter or word counter.
