Punctuating commas in a series is one of the comma rules that people break most frequently.

The Chicago Manual of Style says, “When a conjunction joins the last two elements in a series of three or more, a comma–known as the serial or series comma or the Oxford comma–should appear before the conjunction.”

Wha?

Let’s break that down Grammar Kop style.

There are two main parts to this rule.

1. Our series includes three or more elements.

2. The final two elements in our series are separated by a conjunction (the two most common conjunctions are “and” and “or”).

 

Let’s look at an example.

We’ve got three or more elements in a series that we want to include a sentence. Let’s use the colors of the American flag for this example.

Example: The colors of the American flag are red white and blue.

So, we have a series of three or more elements in a sentence, and the final two words are joined by a conjunction (“and”). So, how do we punctuate it?

It’s common for people to mistakenly punctuate this sentence as follows: The colors of the American flag are red, white and blue.

But, this incorrect because our rule says that if the final two elements in series are joined by “and,” then we need to separate those elements with a comma.

Here’s the correct way to punctuate this sentence: The colors of the American flag are red, white, and blue.

 

See?

Easy peasy!