A run-on sentence is a sentence that goes on and on and needs to be broken up. Run-on sentences occur when two or more independent clauses are improperly joined. (We talked about clauses in Text: Parts of a Sentence.) One type of run-on that you’ve probably heard of is the comma splice, in which two independent clauses are joined by a comma without a coordinating conjunction (and, or, but, etc.).

Let’s look at a few examples of run-on sentences:

• Often, choosing a topic for a paper is the hardest part it’s a lot easier after that.
• Sometimes, books do not have the most complete information, it is a good idea then to look for articles in specialized periodicals.
• She loves skiing but he doesn’t.

All three of these have two independent clauses. Each clause should be separated from another with a period, a semicolon, or a comma and a coordinating conjunction:

• Often, choosing a topic for a paper is the hardest part. It’s a lot easier after that.
• Sometimes, books do not have the most complete information; it is a good idea then to look for articles in specialized periodicals.
• She loves skiing, but he doesn’t.

Common Causes of Run-Ons

We often write run-on sentences because we sense that the sentences involved are closely related and dividing them with a period just doesn’t seem right. We may also write them because the parts seem to short to need any division, like in “She loves skiing but he doesn’t.” However, “She loves skiing” and “he doesn’t” are both independent clauses, so they need to be divided by a comma and a coordinating conjunction—not just a coordinating conjunction by itself.

Another common cause of run-on sentences is mistaking adverbial conjunctions for coordinating conjunctions. For example if we were to write, “She loved skiing, however he didn’t,” we would have produced a comma splice. The correct sentence would be “She loved skiing; however, he didn’t.”

Fixing Run-On Sentences

Before you can fix a run-on sentence, you’ll need to identify the problem. When you write, carefully look at each part of every sentence. Are the parts independent clauses, or are they dependent clauses or phrases? Remember, only independent clauses can stand on their own. This also means they have to stand on their own; they can’t run together without correct punctuation.

Let’s take a look at a few run-on sentences and their revisions:

1. Most of the hours I’ve earned toward my associate’s degree do not transfer, however, I do have at least some hours the University will accept.
2. The opposite is true of stronger types of stainless steel they tend to be more susceptible to rust.
3. Some people were highly educated professionals, others were from small villages in underdeveloped countries.

Let’s start with the first sentence. This is a comma-splice sentence. The adverbial conjunction however is being treated like a coordinating conjunction. There are two easy fixes to this problem. The first is to turn the comma before however into a period. If this feels like too hard of a stop between ideas, you can change the comma into a semicolon instead.

• Most of the hours I’ve earned toward my associate’s degree do not transfer. However, I do have at least some hours the University will accept.
• Most of the hours I’ve earned toward my associate’s degree do not transfer; however, I do have at least some hours the University will accept.

The second sentence is a run-on as well. “The opposite is true of stronger types of stainless steel” and “they tend to be more susceptible to rust.” are both independent clauses. The two clauses are very closely related, and the second clarifies the information provided in the first. The best solution is to insert a colon between the two clauses:

The opposite is true of stronger types of stainless steel: they tend to be more susceptible to rust.

What about the last example? Once again we have two independent clauses. The two clauses provide contrasting information. Adding a conjunction could help the reader move from one kind of information to another. However, you may want that sharp contrast. Here are two revision options:

• Some people were highly educated professionals, while others were from small villages in underdeveloped countries.
• Some people were highly educated professionals. Others were from small villages in underdeveloped countries.