Punctuation: Fragments/Run-ons/Comma Splices

Some writers may write sentences that contain two complete ideas, punctuated only with a comma or with no punctuation at all. Both are wrong.

A complete sentence (also known as an independent clause) is a sentence that can stand on its own.

A run-on sentence, or a comma splice, occurs when two complete sentences are written together with no punctuation or with only a comma to separate them.

Look at the sentences below. They are examples of run-on sentences and comma splices.

  1.  She walked the dog he fed the cat.
  2. She walked the dog, he fed the cat. [comma splice]
  3. I’ve always wanted to go to Reno it’s wonderful there.
  4. I’ve always wanted to go to Reno, it’s wonderful there. [comma splice]
  5. My father designs and installs wind turbines he travels all over the Saudi Arabia as an energy consultant.

    Notice that we have two ideas in two independent clauses:
    My father installs and designs wind turbines.
    He travels all over Saudi Arabia as an energy consultant.

To fix a run-on sentence, determine where one MAIN IDEA ends and another one begins. Run-on sentences can be corrected in 3 ways:

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1. You can insert a period to make the two complete sentences separate.


She walked the dog. He fed the cat.

2. You can insert a semi-colon. Only use a semi-colon if the two sentences are closely related.


I’ve always wanted to go to Reno; it’s wonderful there.

3. You can add a word such as and or therefore after inserting a comma or a semi-colon.

These words will need a comma before the word: and, but, for, or, nor, yet, so.

Words such as however, nevertheless, therefore, finally, etc. will need a semi-colon and a comma.


She walked the dog, and he fed the cat.

I’ve always wanted to go to Reno; however, I haven’t gone yet.

Try some practice exercises:

Practice Exercise: Run-ons - Comma Splices - Fused Sentences (Purdue OWL)

Exercises at Grammar Bytes! (Robin L. Simmons)  


Adapted from Purdue University’s Writing Website.

Last updated December 17, 2015