c. Run-On Sentences

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What is a run-on sentence?

A run-on sentence happens when we combine two or more complete ideas without joining them correctly. Not all long sentences are run-ons. A sentence can be many lines and still be correct if all its parts are connected with the correct punctuation and connecting words.

A comma is not enough to correctly join two complete thoughts or independent clauses. Using a comma to join complete thoughts is a common type of run-on sentence error called a comma splice. Another type of run-on sentence is a fused sentence. A fused sentence occurs when two complete sentences are joined without even a comma. Fused sentences often sound very rushed.

Example 1

  • Fused sentence: Driverless cars with drivers in them are becoming common companies must be test driving the technology.
  • Comma splice: Driverless cars with drivers in them are becoming common, companies must be test driving the technology.

Fixing run-on sentences

There are several options for fixing a run-on sentence. We can keep the two complete ideas together in one sentence, or we can separate them into two sentences.  If we keep them together, we can add a word to clarify the connection between the two ideas, or, if the connection is already obvious, we can connect them with the right punctuation.  Punctuation alone can technically fix a run-on; however, if readers are likely to miss the connection between the two ideas, a connecting word will be important as well.  There are several types of connecting words, each of which needs different punctuation. We can consider which option best helps the reader absorb the ideas and see their relationship.

Use a period to separate the ideas

Adding a period will correct the run-on by creating two separate sentences.  This allows the reader to absorb the ideas one at a time.  This can be a good option if the connection between the ideas is clear, if the combination is difficult to follow, and if the piece of writing does not already have too many short sentences. It’s worth considering the other options as well before deciding to fix a run-on with a period.

Example 2

  • Run-on: There were no seats left, we had to stand in the back.
  • Complete sentence: There were no seats left. We had to stand in the back.

Use a semi-colon to keep closely related ideas together

A semi-colon can be used to connect two complete ideas or independent clauses in one sentence. Two closely related ideas can stay together this way without any additional words.  This is a good option as long as it is clear how the two ideas relate.

Example 3

  • Run-on: The accident closed both lanes of traffic we waited an hour for the wreckage to be cleared.
  • Complete sentence: The accident closed both lanes of traffic; we waited an hour for the wreckage to be cleared.

Use a coordinating conjunction

You can also fix run-on sentences by adding a comma and a coordinating conjunction. A coordinating conjunction acts as a link between two independent clauses.

These are the seven coordinating conjunctions that you can use: for, and, nor, but, or, yet, and so. Choose one that shows the relationship between the ideas when you want to link the two independent clauses. The acronym FANBOYS will help you remember this group of coordinating conjunctions. In the example below, we correct the run-on by adding the coordinating conjunction but between the two independent clauses.

Example 4

  • Run-on: The new printer was installed, no one knew how to use it.
  • Complete sentence: The new printer was installed, but no one knew how to use it.

Use a conjunctive adverb

Another kind of connecting word or transition word is a conjunctive adverb such as “however,” “therefore,” “thus,” “also,” and “similarly.” A sentence with one of these words will still need a semi-colon in between the independent clauses. After the semicolon, add the conjunctive adverb and follow it with a comma. In the example below, we correct the run-on using the conjunctive adverb however.

Example 5

  • Run-on: The project was put on hold we didn’t have time to slow down, so we kept working.
  • Complete sentence: The project was put on hold; however, we didn’t have time to slow down, so we kept working.

Use a dependent word to emphasize one idea over another

Dependent words such as because and although, also called subordinators, can show a relationship between two independent clauses. If we put a dependent word in front of a clause, we have a dependent clause.  That means that the clause is not a complete thought on its own: the dependent word signals that we need to connect it to an independent clause.

A dependent word signals that the main point of the sentence lies elsewhere. It de-emphasizes the clause it goes with.

If a sentence starts with a dependent clause, put a comma before the independent clause starts. If the dependent word comes in the middle of the sentence no comma is used.  In the examples below, we correct the run-ons using the dependent words although and because.

Example 6

  • Run-on: We took the elevator, the others still got there before us.
  • Complete sentence: Although we took the elevator, the others got there before us.


  • Run-on: Cobwebs covered the furniture, the room hadn’t been used in years.
  • Complete sentence: Cobwebs covered the furniture because the room hadn’t been used in years.


Exercise: Find and fix the run-on sentences in the following passages.

  1. The report is due on Wednesday but we’re flying back from San Diego that morning. I told the project manager that we would be able to get the report to her later that day she suggested that we come back a day early to get the report done and I told her we had meetings until our flight took off. We e-mailed our contact who said that they would check with his boss, she said that the project could afford a delay as long as they wouldn’t have to make any edits or changes to the file our new deadline is next Friday.
  2. Alma tried getting a reservation at the restaurant, but when she called they said that there was a waiting list so she put our names down on the list when the day of our reservation arrived we only had to wait thirty minutes because a table opened up unexpectedly which was good because we were able to catch a movie after dinner in the time we’d expected to wait to be seated.
  3. Without a doubt, my favorite artist is Leonardo da Vinci, not because of his paintings but because of his fascinating designs, models, and sketches, including plans for scuba gear, a flying machine, and a life-size mechanical lion that actually walked and moved its head. His paintings are beautiful too, especially when you see the computer-enhanced versions researchers use a variety of methods to discover and enhance the paintings’ original colors, the result of which are stunningly vibrant and yet delicate displays of the man’s genius.


“Run-On Sentences” was adapted from “13.5: Run-on Sentences ” of  How Arguments Work – A Guide to Writing and Analyzing Texts in College (Mills), used according to creative commons CC BY-NC-SA 4.0.



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UNM Core Writing OER Collection Copyright © 2023 by University of New Mexico is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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