How to Fix Run-On Sentences: 5 Methods + Practice Exercises

I used to mark every run-on sentence in my students’ papers with a red circle and a frustrated question mark. Then one student asked me, “But why is it wrong if you understand what I meant?” That question forced me to be clearer: run-on sentences aren’t wrong because they’re ugly or careless — they’re wrong because they hide the breaks between ideas. When your reader has to guess where one thought ends and the next begins, you’ve handed them work they shouldn’t have to do. A run-on sentence is laziness in disguise.

I’ll show you exactly what run-on sentences are, why they happen, the five ways to fix them, and what to do about the trickiest variations (dependent clauses, comma splices, fused sentences). By the end, you’ll not only spot run-ons in your own writing — you’ll know which fix works best for each situation.

What Is a Run-On Sentence? (Definition)

A run-on sentence is two or more independent clauses that are joined together without proper punctuation or a conjunction. An independent clause is a complete thought — it has a subject and a verb and can stand alone as a sentence on its own.

The trap students fall into is thinking a run-on is just “a long sentence.” That’s not true. A 30-word sentence can be perfectly correct if it has proper punctuation. A 15-word sentence can be a run-on if it joins independent clauses incorrectly.

Two Types of Run-On Sentences

Type 1: Comma Splice

A comma splice happens when two independent clauses are joined with only a comma — no conjunction after it.

✗ Example: I love to read, I could spend hours lost in a good book.

The comma by itself is not strong enough to hold two independent clauses together. A comma’s job is to separate items in a list or to set off introductory phrases — not to join complete thoughts.

Type 2: Fused Sentence

A fused sentence joins two independent clauses with no punctuation at all — not even a comma.

✗ Example: I love to read I could spend hours lost in a good book.

This is harder to spot when reading aloud because you naturally pause between ideas. But on the page, it’s a clear break in structure.

The Dependent Clause Trick

Here’s where it gets tricky: if one of your clauses is dependent (can’t stand alone), there’s no run-on, even if there’s no comma between the clauses.

✗ Incorrect (run-on with dependent clause): Although I love to read I don’t have the time.

✓ Correct (dependent clause, needs a comma but not a conjunction): Although I love to read, I don’t have the time.

The phrase “Although I love to read” is a dependent clause — it depends on “I don’t have the time” to make complete sense. So you need a comma (to mark the break), but not a conjunction or semicolon.

Why Run-On Sentences Are a Problem

Three reasons run-ons hurt your writing:

1. They confuse readers. Without a clear break between ideas, your reader has to pause and re-read to understand where one thought ends and the next begins.
2. They hide relationships between ideas. By not choosing a punctuation mark, you don’t tell your reader: “These ideas are equal” (period or semicolon), or “This one depends on that one” (comma with dependent clause), or “Here’s a contrast” (comma with “but”).
3. They signal carelessness. In academic or professional writing, a run-on sentence suggests the writer didn’t proofread or doesn’t know the rules.

The Five Fixes for Run-On Sentences

Fix 1: Split Into Two Sentences (Period)

The simplest fix is to put a period between the two independent clauses, creating two complete sentences.

Run-on (Comma Splice)	Fixed (Period)
I went to the store, I bought some milk.	I went to the store. I bought some milk.
She was tired, she stayed up late anyway.	She was tired. She stayed up late anyway.
The meeting was long, it was also productive.	The meeting was long. It was also productive.

When to use this fix: When the two ideas are separate and don’t need a special relationship signal. Or when you want to give each idea its own emphasis.

Fix 2: Add a Coordinating Conjunction (Comma + FANBOYS)

A coordinating conjunction (for, and, nor, but, or, yet, so) can join two independent clauses if preceded by a comma.

Run-on	Fixed (Comma + Conjunction)
I went to the store I bought milk.	I went to the store, and I bought milk.
She was tired she stayed up late.	She was tired, but she stayed up late.
The meeting was long it was productive.	The meeting was long, and it was productive.

When to use this fix: When you want to show that the two ideas are equal and related. The conjunction tells your reader the exact relationship: “and” = addition, “but” = contrast, “so” = cause/effect.

Fix 3: Use a Semicolon

A semicolon shows that two independent clauses are closely related and belong in the same sentence.

Run-on	Fixed (Semicolon)
I went to the store I bought milk.	I went to the store; I bought milk.
She was tired she stayed up late.	She was tired; she stayed up late.
I have a lot of work I don’t have time for TV.	I have a lot of work; I don’t have time for TV.

When to use this fix: When the two ideas are closely connected but you want them in one sentence. The semicolon says: “These belong together, but they’re still independent ideas.”

Caution: The semicolon is formal. Use it sparingly, especially in creative writing. Overuse makes your prose feel stiff.

Fix 4: Semicolon + Conjunctive Adverb

A conjunctive adverb (however, therefore, furthermore, moreover, nevertheless, in addition) can join two independent clauses if preceded by a semicolon and followed by a comma.

Run-on	Fixed (Semicolon + Adverb)
She was tired she stayed up late.	She was tired; however, she stayed up late.
He studied hard he still failed.	He studied hard; nevertheless, he still failed.
The job is difficult it’s rewarding.	The job is difficult; however, it’s rewarding.

When to use this fix: When you want to signal a more sophisticated relationship between ideas — contrast, concession, addition, or cause/effect. Conjunctive adverbs are more formal than simple coordinating conjunctions.

Fix 5: Subordination (Make One Clause Dependent)

You can also fix a run-on by turning one independent clause into a dependent clause using a subordinating conjunction (because, although, if, when, since, unless, while, etc.).

Run-on	Fixed (Subordination)
I went to bed I was tired.	Because I was tired, I went to bed.
She stayed up late she wanted to finish the project.	She stayed up late because she wanted to finish the project.
The restaurant was closed we went somewhere else.	Since the restaurant was closed, we went somewhere else.

When to use this fix: When one idea is the reason for or condition of the other. Subordination shows that the ideas are not equal — one explains or depends on the other.

How to Identify Independent vs. Dependent Clauses

The key to fixing run-ons is knowing when you have two independent clauses. Here’s the test:

For each clause, ask: “Could this stand alone as a complete sentence?”

• “I went to the store” — Yes, it’s a complete sentence. It’s independent.
• “I bought some milk” — Yes, it’s a complete sentence. It’s independent.
• “Because I was tired” — No, it’s incomplete. It needs “I went to bed.” It’s dependent.
• “Although I love to read” — No, it’s incomplete. It needs “I don’t have the time.” It’s dependent.

Common Run-On Mistakes (With Fixes)

✗ Incorrect: The students studied hard, they passed the exam with flying colors.

✓ Correct: The students studied hard, and they passed the exam with flying colors.

Why: Comma splice. Add a conjunction (and) to show both ideas are part of the same result.

✗ Incorrect: I enjoy swimming in the summer it’s my favorite way to stay cool.

✓ Correct: I enjoy swimming in the summer because it’s my favorite way to stay cool.

Why: Fused sentence. Add a subordinating conjunction (because) to show that the second idea explains the first.

✗ Incorrect: The weather was cold the children still played outside.

✓ Correct: Although the weather was cold, the children still played outside.

Why: Fused sentence. Use subordination (although) to show the contrast between the two ideas.

✗ Incorrect: She wanted to attend the concert, however, she didn’t have a ticket.

✓ Correct: She wanted to attend the concert; however, she didn’t have a ticket.

Why: The conjunctive adverb “however” needs a semicolon before it, not a comma.

Example Sentences

Example: This is a correct sentence with a period separating two complete thoughts: “I went to the store. I bought some milk.” Each clause can stand alone independently.

Example: This shows the comma + conjunction fix: “I went to the store, and I bought some milk.” The conjunction clearly links the ideas.

Example: This uses a semicolon: “She was tired; she stayed up late anyway.” The semicolon shows the ideas are closely related but independent.

Example: This uses a subordinating conjunction: “Because I was tired, I went to bed early.” The subordination makes the relationship between ideas clear.

Example: This shows a conjunctive adverb: “He studied hard; however, he still failed.” The semicolon + conjunctive adverb shows contrast.

Practice Exercise: Identify and Fix

Try fixing these run-on sentences. Use any of the five methods above:

1. The project is due tomorrow my team hasn’t started yet.
2. I wanted to call you the phone was broken.
3. He runs every morning it helps him stay healthy.
4. The movie was boring we left halfway through.
5. She’s very talented, she never practices.

Sample Fixes:

1. The project is due tomorrow, and my team hasn’t started yet. (or use a semicolon: “tomorrow; my team”)
2. Because 🔊 🎤 the phone was broken, I couldn’t call you. (or: “I wanted to call you, but the phone was broken.”)
3. He runs every morning; it helps him stay healthy. (or: “He runs every morning, which helps him stay healthy.”)
4. The movie was boring, so we left halfway through.
5. She’s very talented; however, she never practices.

Sample Dialogues

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