Run-on sentences occur when two or more independent clauses are improperly joined. Often, in a run-on sentence, the independent clauses are simply joined without any punctuation or a coordinating conjunction. Another 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 (remember, FANBOYS):

• 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.

A run-on sentence should not just be defined as a sentence that goes on and on. Not every long sentence is a run-on sentence. For example, look at this quote from The Great Gatsby:

Its vanished trees, the trees that had made way for Gatsby’s house, had once pandered in whispers to the last and greatest of all human dreams; for a transitory enchanted moment man must have held his breath in the presence of this continent, compelled into an aesthetic contemplation he neither understood nor desired, face to face for the last time in history with something commensurate to his capacity for wonder.

If you look at the punctuation, you’ll see that this quote is a single sentence. F. Scott Fitzgerald used commas and semicolons in such a way that, despite its great length, it’s grammatically sound, as well. Length is no guarantee of a run-on sentence.

Common Causes of Run-on Sentences

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 too short to need any division, as 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 and revise, 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.

There are five ways you can fix a run-on sentence or comma splice:

1. Change the comma in the comma splice to a semicolon (or add a semicolon between the independent clauses).
2. Change the comma in the comma splice to a colon, but only if the two clauses are very closely related and the second one seems to be explaining or clarifying the first.
3. Add a coordinating conjunction (FANBOYS) after the comma in the comma splice.
4. Change the comma to a period and separate the two independent clauses into two separate sentences.
5. Rewrite the sentence entirely so the run-on sentence is no longer a problem.

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

• 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.

This is a comma splice. The adverbial conjunction “however” is being treated like a coordinating conjunction (remember, FANBOYS). There are two easy fixes to this problem. The first is to turn the comma before “however” into a period:

• 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.

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.

Let’s take a look at another sentence.

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

This 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. Since 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 (although a semicolon is grammatically correct as well):

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

Let’s try another one.

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

In this 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.

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