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Run-On Sentences

Run-on sentences occur when writers try to combine more than one idea into a single sentence. They cause confusion because readers are not sure when one idea ends and the next one begins. Read our entry and test your knowledge with our quiz!


Commas are some of the most common punctuation marks, and perform many different functions in sentences. You should use commas

To list things:

Example: I need to buy eggs, tomatoes, and milk.

To separate two parts of a compound sentence:

Example: I like football a lot, but baseball is my favorite sport.

Note, however, that you will not use a comma before any conjunction. Only add a comma before a coordinating conjunction, which is a conjunction that connects two complete statements.

Example: I will send the file to you and mail the forms to the IRS. 

This example is correct because the first subject in the sentence, "I," carries over to the second part of the sentence. 

After introductory phrases that kick off a sentence:

Example: Meanwhile, Kate was still stuck in traffic.

Example: First, whisk two eggs.

Before introducing a quotation:

Example: Vincent van Gogh once said, “The sight of the stars makes me dream.”

At the beginning of letters:

Example: Dear Santa, This year…

Within an address:

Example: The President lives at 1600 Pennsylvania Avenue, Washington, DC.