Correcting Run-Ons — I can recognize and correct run-on sentences or missing punctuation in supported editing tasks.

Why Sentences Need Boundaries

Think about how you talk. When you speak, you pause between ideas. You take a breath. Those pauses help the person listening know when one thought ends and a new one begins. Writing works the same way — but instead of pauses, we use punctuation marks like periods and commas. When a sentence runs two complete thoughts together without the right punctuation, it is called a run-on sentence. Run-on sentences are hard to read because the reader cannot tell where one idea stops and the next one starts. This lesson will help you spot run-ons and fix them.

The big question we will answer in this lesson is simple: when two complete thoughts end up in the same sentence, how do you fix it? There are a few easy ways, and we will look at each one.

Key Words and Definitions

Before we practice fixing run-on sentences, let's learn a few key words. A complete sentence has a subject (who or what the sentence is about) and a verb (what that subject does) and expresses a complete thought. A run-on sentence happens when two complete thoughts are stuck together without the right punctuation. There are two common types of run-ons: a fused sentence (no punctuation at all between the two thoughts) and a comma splice (only a comma between the two thoughts, with no joining word). Learning to spot these two errors is the first step to fixing them.

Visual Explanation — Anatomy of a Run-On

The diagram above shows all the main ideas from this lesson in one picture. The two error types at the top have the same problem: two complete thoughts with no proper boundary between them. The four fixes at the bottom each solve the problem in a slightly different way. A period makes two separate sentences — the clearest and simplest fix. A semicolon shows that the two ideas are closely connected. A comma with a joining word shows how the two ideas relate (for example, "but" shows contrast, and "so" shows a result). Adding a word like "because" or "when" at the start of one thought makes it clear that one idea supports the other.

How to Fix Run-Ons — Four Simple Strategies

There are four easy ways to fix a run-on sentence. Each one works by putting a clear boundary between two complete thoughts. Let's look at each fix one at a time, with simple examples from everyday life.

Fix 1 — Use a Period

The easiest fix is to put a period between the two complete thoughts and start the second one with a capital letter. This makes two separate sentences. For example: I went to the store I bought milk. → I went to the store. I bought milk. This fix is always correct and is a great place to start.

Fix 2 — Use a Semicolon

A semicolon (;) can join two complete thoughts that are closely related. You do not need a joining word with a semicolon. For example: I went to the store I bought milk. → I went to the store; I bought milk. Use a semicolon when the two ideas are very closely connected and you want to keep them in the same sentence.

Fix 3 — Use a Comma Plus a Joining Word (FANBOYS)

A comma alone between two complete thoughts is an error. But a comma plus a joining word works correctly. The seven joining words are: for, and, nor, but, or, yet, so. You can remember them with the word FANBOYS. For example: I went to the store I bought milk. → I went to the store, and I bought milk. The joining word shows how the two ideas connect. "But" shows contrast. "So" shows a result. "And" adds information.

Fix 4 — Add a Connecting Word to the Start

You can also add a word like "because," "when," "since," or "although" to the beginning of one thought. This makes that thought lean on the other one, showing how the ideas are connected. For example: I went to the store I needed milk. → I went to the store because I needed milk. This is a good fix when one idea explains the reason for the other.

Choosing the Right Fix

All four fixes are correct. How do you choose which one to use? The best fix depends on how the two ideas relate to each other. The flowchart and table below will help you decide.

Worked Example — Editing a Paragraph for Run-Ons

The following worked example shows how to find and fix run-on sentences in a short paragraph. The paragraph is about a busy morning at work — the kind of everyday situation many people write about. Notice how each step starts by checking if there are two complete thoughts before choosing a fix.

Strengths and Limits of Each Fix

Each fix works well, but each one also has times when it is not the best choice. The table below shows the good points and things to watch out for with each fix. Good writers mix and match to keep their writing clear and interesting.

What You Can Do Next

Fixing run-on sentences is an important first step in writing clearly. Once you feel comfortable spotting and fixing run-ons, you will be ready to work on other writing skills. The table below shows how what you learned in this lesson connects to the next things you can learn.

Every skilled writer started exactly where you are now — learning to put the right punctuation in the right place. As you practice, fixing run-ons will become second nature. You will start to notice them in things you read every day, like emails, signs, and notes. That awareness is a sign that your writing skills are growing.

Practice Problems

Try these five practice problems. Each one asks you to find and fix a run-on sentence using what you have learned. The problems use everyday situations so you can see how these skills work in real life.

Lesson Summary