What Is a Run-On Sentence? Types, Examples, and How to Fix Them
By Shihab Mia July 13, 2026 7 min read
Quick answer
A run-on sentence is one that joins two or more independent clauses (complete thoughts that could each stand alone) without correct punctuation or a joining word. The two main types are the fused sentence (no punctuation at all between the clauses) and the comma splice (two independent clauses joined by only a comma). You can fix almost any run-on in one of four ways: split it into two sentences with a period, add a comma plus a coordinating conjunction (FANBOYS), join the clauses with a semicolon, or make one clause subordinate. Length alone does not make a sentence a run-on.
Run-on sentences are one of the most common writing errors flagged in school essays, business emails, and online posts, yet the name confuses people. Many writers assume a run-on is simply a sentence that is too long. That is a myth. A run-on is about structure, not word count. A twelve-word sentence can be a run-on, and a fifty-word sentence can be perfectly correct. This guide explains exactly what a run-on is, shows the two types with clear examples, and walks you through the four fixes step by step.
What is a run-on sentence, exactly?
A run-on sentence occurs when two or more independent clauses are joined without the correct punctuation or a conjunction. An independent clause is a group of words that contains a subject and a verb and expresses a complete thought, so it could stand alone as its own sentence. When you push two of these complete thoughts together without the right connector, the reader loses the boundary between ideas.
Consider this example: I finished the report I sent it to my manager. Both "I finished the report" and "I sent it to my manager" are complete thoughts. Slammed together with nothing between them, they form a run-on. The reader has to guess where one idea ends and the next begins.
The length myth
Length does not make a sentence a run-on. The team spent the entire quarter refining the launch plan, and after several late nights they finally shipped a product that customers genuinely loved. That sentence is long, but it is grammatically correct because the clauses are joined properly with a comma and the conjunction "and."
What are the two types of run-on sentences?
The two main types are the fused sentence and the comma splice. They differ only in what sits (or does not sit) between the independent clauses.
1. The fused sentence
A fused sentence has no punctuation at all between the two independent clauses. The thoughts run directly into each other with nothing to separate them.
- Fused: The rain stopped we went outside.
- Fused: She studied all night the exam was still hard.
- Fused: Our flight was delayed we missed the connection.
2. The comma splice
A comma splice joins two independent clauses with only a comma. A comma is not strong enough to link two complete thoughts on its own, so this still counts as a run-on even though punctuation is present.
- Comma splice: The rain stopped, we went outside.
- Comma splice: She studied all night, the exam was still hard.
- Comma splice: Our flight was delayed, we missed the connection.
Fused sentence vs comma splice at a glance
| Type | What joins the clauses | Example | Correct? |
|---|---|---|---|
| Fused sentence | Nothing at all | The rain stopped we went outside. | No |
| Comma splice | Only a comma | The rain stopped, we went outside. | No |
| Fixed version | Comma plus conjunction | The rain stopped, so we went outside. | Yes |
How do you fix a run-on sentence?
You can fix almost any run-on in one of four ways: split it into two sentences with a period, add a comma plus a coordinating conjunction, join the clauses with a semicolon, or make one clause subordinate. Pick the method that best fits the relationship between your two ideas.
Fix 1: Split into two sentences with a period
The simplest fix is to give each complete thought its own sentence. Use this when the two ideas are strong on their own and do not need a tight connection.
- Before: The rain stopped we went outside.
- After: The rain stopped. We went outside.
Fix 2: Add a comma plus a coordinating conjunction (FANBOYS)
Use a comma followed by one of the seven coordinating conjunctions, easily remembered as FANBOYS: for, and, nor, but, or, yet, so. This keeps both ideas in one sentence and signals how they relate.
- Before: The rain stopped we went outside.
- After: The rain stopped, so we went outside.
Fix 3: Join the clauses with a semicolon
A semicolon links two closely related independent clauses without a conjunction. Use it when the two thoughts are balanced and clearly connected in meaning.
- Before: She studied all night the exam was still hard.
- After: She studied all night; the exam was still hard.
Fix 4: Make one clause subordinate
Turn one independent clause into a dependent clause by adding a subordinating word such as because, although, when, since, while, or if. This shows which idea depends on the other and often reads the most naturally.
- Before: Our flight was delayed we missed the connection.
- After: Because our flight was delayed, we missed the connection.
Worked example: fixing a run-on step by step
Take this run-on: The printer jammed the meeting started in five minutes I panicked. It contains three independent clauses fused together. Here is how to repair it.
- Find the independent clauses. Ask which word groups have a subject and verb and could stand alone: "The printer jammed," "the meeting started in five minutes," and "I panicked." That is three complete thoughts with nothing between them.
- Decide how the ideas relate. The jam and the tight timing together caused the panic, so there is a cause-and-effect chain worth showing.
- Choose your fixes. Make the first clause subordinate to show cause, and separate the reaction cleanly.
- Rewrite: "Because the printer jammed and the meeting started in five minutes, I panicked."
- Read it aloud. If each pause feels natural and no two complete thoughts collide, the run-on is gone.
Reading your work aloud is one of the fastest manual checks. When you hear yourself run two full statements together with no breath or connector, that spot is almost always a run-on. If you want a second pair of eyes, a free sentence checker can flag fused sentences and comma splices automatically before you hit send.
Common mistakes and good to know
Most run-on trouble comes from a handful of predictable habits. Watch for these.
- Confusing length with error. A long sentence is not automatically a run-on. Check whether independent clauses are joined correctly, not how many words there are.
- Using a comma before "however," "therefore," or "then." These are conjunctive adverbs, not FANBOYS conjunctions. I was tired, however I kept working is a comma splice. Use a semicolon: I was tired; however, I kept working.
- Assuming any comma will do. A comma alone cannot join two complete thoughts. It needs a coordinating conjunction to do that job.
- Forgetting the comma before FANBOYS. When a coordinating conjunction joins two independent clauses, put a comma before it: I called, but no one answered.
- Over-splitting. Turning every idea into a short choppy sentence fixes run-ons but can make writing feel robotic. Vary your sentence structure. For more on where sentences fit, see how many sentences in a paragraph.
Good to know
Not every clause that starts with "and" or "but" is wrong. Starting a sentence with a coordinating conjunction is stylistically acceptable in most modern writing. If you have wondered about that, read our take on whether you can start a sentence with "and".
Run-on sentences vs sentence fragments
A run-on has too much: two or more complete thoughts jammed together. A fragment has too little: a piece of a sentence missing a subject, a verb, or a complete thought, such as Because the printer jammed. on its own. They are opposite problems. Knowing which one you have tells you whether to break a sentence apart (run-on) or complete it (fragment).
Run-on vs fragment
| Problem | What is wrong | Example |
|---|---|---|
| Run-on | Two or more complete thoughts joined incorrectly | The printer jammed I panicked. |
| Fragment | An incomplete thought standing alone | Because the printer jammed. |
| Correct | Complete thoughts joined or completed properly | Because the printer jammed, I panicked. |
Run-on sentences look intimidating, but they come down to one idea: two complete thoughts need a proper connector between them. Once you can spot an independent clause, you can fix any run-on with a period, a comma plus a FANBOYS conjunction, a semicolon, or a subordinating word. Remember that length is never the test. Structure is. Learn the two types, keep the four fixes handy, and proofread by reading aloud, and your writing will stay clear and correct.