Quick Answer
A comma splice joins two complete sentences with just a comma (“I like tea, she likes coffee”). A run-on sentence joins them with no punctuation at all (“I like tea she likes coffee”). Fix either by adding a period, a semicolon, or a conjunction like and or but.
A comma splice and a run-on sentence are two of the most common sentence-level errors in English writing. Both happen when two complete sentences get joined incorrectly — the difference is just how they’re (mis)joined.
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What Is a Comma Splice?
A comma splice happens when two complete sentences (independent clauses) are joined with only a comma, and no conjunction.
- Incorrect: I love hiking, it’s my favorite hobby.
- Incorrect: The store was closed, we went home instead.
Each half of these sentences could stand alone as its own complete sentence — which is exactly why a comma alone isn’t strong enough to join them.
What Is a Run-On Sentence?
A run-on sentence (also called a fused sentence) joins two complete sentences with no punctuation and no conjunction at all.
- Incorrect: I love hiking it’s my favorite hobby.
- Incorrect: The store was closed we went home instead.
Grammar note: A run-on sentence isn’t defined by length. A short sentence can be a run-on, and a long sentence with correct punctuation is not.
Four Ways to Fix Them
Both errors are fixed the same four ways:
- Split into two sentences. I love hiking. It’s my favorite hobby.
- Add a coordinating conjunction after the comma. I love hiking, and it’s my favorite hobby.
- Use a semicolon. I love hiking; it’s my favorite hobby.
- Make one clause dependent. Because I love hiking, it’s my favorite hobby.
Comma Splice vs. Run-On at a Glance
| Error | What Joins the Clauses | Example |
|---|---|---|
| Comma splice | A comma only | I like tea, she likes coffee. |
| Run-on sentence | Nothing at all | I like tea she likes coffee. |
When a Comma Splice Is Allowed
In casual or literary writing, short comma splices are sometimes used deliberately for rhythm or effect: “I came, I saw, I conquered.” This is a stylistic choice, not standard practice — avoid it in formal or academic writing.
Common Mistakes
- Assuming a comma is always enough to join two sentences. It only works with a conjunction (and, but, or, so, yet) after it.
- Overusing semicolons as a fix. A semicolon works, but breaking into two sentences often reads more naturally.
- Confusing a run-on with a long sentence. Length isn’t the issue — missing punctuation between independent clauses is.
- Using “however” or “therefore” like a conjunction. “I was tired, however I kept working” is a comma splice — use a semicolon before however: “I was tired; however, I kept working.”
Frequently Asked Questions
What is a comma splice, simply put?
It’s when two complete sentences are joined with only a comma, without a conjunction. Example: “It was raining, we stayed inside.”
What’s the difference between a comma splice and a run-on sentence?
A comma splice uses a comma with no conjunction. A run-on sentence uses no punctuation at all between the two complete sentences.
Is a long sentence automatically a run-on?
No. Length has nothing to do with it — a run-on is defined by missing punctuation between independent clauses, not by word count.
Can I ever use a comma splice on purpose?
In casual or creative writing, short comma splices are sometimes used for rhythm. Avoid them in formal or academic writing.
Quick Reference
- Comma splice: two complete sentences joined by only a comma
- Run-on sentence: two complete sentences joined with no punctuation
- Four fixes: split into two sentences, add a conjunction, use a semicolon, or make one clause dependent
Quick Practice
Three quick questions. See what stuck.
1. “The dog barked, the mailman ran.” What is this an example of?
2. “The dog barked the mailman ran.” What is this an example of?
3. Which is a correct fix for “I was tired, however I kept working”?