A comma ( , ) is a piece of punctuation used within a sentence to force a pause or to show a separation.
Use a comma in a list to show separation between items in the list.
Each of these sentences has a list of items. A comma is placed after each item in the list except the very last item.
You need tennis shoes, a tennis racket, and some tennis balls if you want to play the sport.
My favorite foods are grapes, raspberries, carrots, and cookies.
Look at this sentence to see what happens when you don’t use commas with a list:
Tom will bring his binder clips and paper.
At first glance, it looks like Tom is bringing two things – binder clips and paper.
But maybe he is really bringing three things: his binder, clips, and paper.
When you add commas, the sentence looks like this:
Tom will bring his binder, clips, and paper.
Here is are three more sentences that read differently depending on whether or not there are commas:
The man has a horse trailer and truck. In this sentence, the man has two objects.
The man has a horse, trailer, and truck. When you use commas, the man has three objects.
I like fruit juice and cereal for breakfast. – In this sentence, you have two things for breakfast.
I like fruit, juice, and cereal for breakfast. – With the commas, you have three things.
The room was empty except for a piano bench and music. The room holds two things.
The room was empty except for a piano, bench, and music. Now the room has three things in it.
Use commas in a list to make clear the meaning of your sentence.
A list of two words does not need a comma. I ate breakfast and lunch.
Whenever your list has three or more words, you must use a comma after each word except the last one.
I ate breakfast, lunch, and dinner.
I ate breakfast, lunch, dinner, and two snacks.
Some writers don’t put a comma after the item in a list that comes just before and:
I like the colors red, blue and green.
The comma right before and is called an “Oxford comma” because the Oxford University Press uses it.
People who use the Oxford comma say it makes writing clearer. Those who don’t use the Oxford comma say that it isn’t needed. You can decide whether or not you want to use that comma just before the and. The ACT standardized test requires the Oxford Comma. The SAT standardized test doesn’t care one way or the other.