What Is a Run-On Sentence? How to Fix One, With Run-On Sentence Examples and Answers

Fix a run-on sentence by finding its complete thoughts and checking the join between them. You can repair that boundary without cutting a correctly written long sentence into pieces.

What is a run-on sentence, and what should you fix first?

A run-on has complete clauses joined incorrectly. Start by fixing the boundary between them, rather than rewriting everything.

Before: “The bus arrived we boarded.” After: “The bus arrived. We boarded.” Here’s the simplest repair:

In plain language, a run-on sentence means that complete thoughts have run together without the right punctuation or connecting word. Length alone doesn’t make a sentence a run-on. I’d check the join first, even when the sentence looks short.

1. Find the complete thoughts: “The bus arrived” and “we boarded” each work alone.
2. Put a period between them: “The bus arrived. We boarded.”

Run-on sentence definition and examples: Why the error happens

An independent clause has a subject, a verb, and a complete thought. The William H. Hannon Library’s grammar guide explains that it can stand alone as a sentence. In “The bus arrived,” the subject is “The bus” and the verb is “arrived.”

Fused sentence: “The bus arrived we boarded.” Comma splice: “The bus arrived, we boarded.” Both contain complete clauses. The first has no boundary punctuation; the second uses only a comma.

These errors happen when connected ideas feel like one thought, or when you assume a comma is enough. Another cause is treating “however” or “therefore” like “and” or “but.” Purdue OWL shows a semicolon before “however” when it connects independent clauses, followed by a comma.

Two common incorrect joins

Easy run-on sentence examples to check against your own writing

Use this clause-boundary test on your own draft:

Here are run-on sentence examples and answers to compare. Fused: “The rain stopped we left.” Answer: “The rain stopped. We left.” Comma splice: “The rain stopped, we left.” Answer: “The rain stopped, so we left.”

Correct long sentence: “After the rain stopped and the clouds began to clear, we walked through the park, carrying our umbrellas and watching the puddles along the path.” The opening gives timing; “we walked” carries the main thought. There’s no incorrect join.

Don’t use breath length or word count as your test. Look for complete clauses.

1. Locate each subject and verb. In “The rain stopped we left,” they are “The rain” plus “stopped” and “we” plus “left.”
2. Test each clause alone. “The rain stopped” and “We left” are complete sentences.
3. Inspect the join. No punctuation makes this a fused sentence. A comma alone would make it a comma splice.

How to fix a run-on sentence, starting with the simplest repair

Start with “The room was cold I closed the window.” These repairs move from a simple boundary change to a decision about meaning:

Purdue OWL gives the coordinating conjunctions as “and,” “but,” “for,” “or,” “nor,” “so,” and “yet.” Choose the one that expresses your intended connection. UNC’s Writing Center explains that words such as “because” make a clause dependent and show a logical relationship.

For contrast with “however,” use this pattern: “The room was cold; however, I left the window open.” A comma before “however” alone wouldn’t repair the join.

Check your revision with Blurwrite’s free grammar checker for grammar and punctuation issues. Each suggestion names its category and offers a fix to apply or ignore. Review the correction in context so the connection still says what you mean.

1. Use a period and capitalize the next sentence: “The room was cold. I closed the window.” This keeps both statements without naming their relationship.
2. Use a semicolon: “The room was cold; I closed the window.” Both clauses remain complete, but the punctuation keeps them closely connected.
3. Add a comma and a coordinating conjunction: “The room was cold, so I closed the window.” “So” explicitly presents the action as a result.
4. Make one clause dependent: “Because the room was cold, I closed the window.” The cold room becomes the explanation for the main action.

Choose the relationship you mean

What not to do: A long sentence can still be correct

Short run-on: “I called she answered.” Longer, correct sentence: “I called the office after lunch, and the assistant answered my questions about the application before the office closed.” The comma and “and” join its complete clauses.

A shared subject is different: “I opened the document and checked the heading.” This is a compound predicate, meaning one subject performs both actions. You don’t need a comma before “and” here.

Don’t scatter commas through a sentence or put a semicolon before an incomplete thought. “I stayed home; because I felt ill” is wrong. Write “I stayed home because I felt ill.” Don’t split every long sentence either. UW-Madison’s Writing Center distinguishes grammatical errors from sentence sprawl that needs clearer wording.

What is the opposite of a run-on sentence? Not a fragment, which is incomplete. Aim for complete thoughts with correct joins. Before accepting a repair, check: complete clauses, correct connection, preserved meaning.

Length and completeness are different checks

When to ask a teacher, editor, or writing tutor

Ask a person when the relationship between ideas remains unclear, suggestions conflict, or dense prose needs restructuring. Bring your original sentence, intended meaning, and attempted correction.

Deliberate literary effects differ from ordinary formal-writing expectations. If you’re working across languages, our resources for second-language writers offer a relevant starting point. Ask your reviewer whether the correction preserves your meaning, not just whether it shortens the sentence.

Written byPriya AnandEditor for second-language writersUpdated on October 4, 2026