Here is a  simple way to use commas to write crystal-clear sentences when you need your reader to understand items in a series (lists of three or more things).  Without any commas, three or more items in a series run into one another. The result is confusing.

Joe’s first assignments will be to clean the shelves move the filing cabinets put the books in alphabetical order and take the outdated files to the warehouse.

Commas make it clear that each item in the series — in this case, four activities — is separate from the other items.

Joe’s first assignments will be to clean the shelves, move the filing cabinets, put the books in alphabetical order, and take the outdated files to the warehouse.

“Red, white, and blue” is an example of three items in a series. The most common conjunctions for items in a series are the words and and or.

One of the most common punctuation questions is whether to use a comma before the final conjunction in a series of three or more items. This punctuation is sometimes called the serial or series comma.

Without series comma: The store has the shirt in red, blue, green and yellow.

With series comma: The store has the shirt in red, blue, green, and yellow.

In fact, there is no hard-and-fast rule about including or omitting the series comma. Some organizations have rules requiring that you always use the series comma or that you avoid it. Very few journalists use the series comma because omitting it saves column space.

If your organization doesn’t have this rule, we recommend always using the series comma. It makes your writing clearer and makes your life simpler. If you always use the series comma, you’ll never have to pause and ask yourself if your reader will grasp your meaning, and you’ll always be correct.

One more thing: remember that the series comma always goes before the conjunction, and never after it.

Incorrect: Send the company treasurer your last three pay stubs, a copy of your federal tax return and, copies of any form 1099s you might have received.

Correct: Send the company treasurer your last three pay stubs, a copy of your federal tax return, and copies of any form 1099s you might have received.

Finally, here are some sentences without the series comma. Try inserting the series comma in these sentences.

1. The doctor said the condition’s symptoms include itching, hunger and thirst.

2. There are three new team members: Erin Copland, Jennifer Steinblum and Pat Jonas.

3. The valedictorian thanked his parents, Ms. Brown and Mr. Weir.

Next, you’ll find the same three sentences with the series comma. We think you’ll agree that the series comma helps clarify the meaning of each sentence.

1. The doctor said the condition’s symptoms include itching, hunger, and thirst.

2. There are three new team members: Erin Copland, Jennifer Steinblum, and Pat Jonas.

3. The valedictorian thanked his parents, Ms. Brown, and Mr. Weir.

Without the series comma, Sentence 3 could refer to the valedictorian’s thanking either two or four people. The reader is left guessing whether or not Ms. Brown and Mr. Weir are the valedictorian’s parents. The series comma makes it clear that the valedictorian thanked four people.