One of the tricky questions about comma usage is how to use commas in a list of items.
For example, should it be:
I love to eat apples, oranges, and bananas. OR I love to eat apples, oranges and bananas. ???
Technically, both versions are correct. But I prefer the second. I try to make my writing as clear, simple and elegant as possible, and part of my strategy is to eliminate anything unnecessary. The final comma in a simple list is unnecessary, so I leave it out.
Sometimes, though, you need to add the final comma to preserve your meaning. Here’s an example I love from Ben Yagoda’s book How to Not Write Bad (the title is a joke, by the way, to demonstrate how jarring bad writing can be).
Imagine a student writing about what he is grateful for. Yagoda shows how the final comma in a list is sometimes not superfluous. There’s a big difference between:
I am thankful for my parents, Ayn Rand, and God. AND I am thankful for my parents, Ayn Rand and God.
In the first statement, the student is clearly listing three things for which he is thankful. In the second, he appears to be claiming he’s the offspring of Ayn Rand and God. That final comma sometimes makes a crucial difference in meaning.
You often also use a final comma in a list of items when the items are longer. Here’s an example:
He returned many items from the storeroom to their original owners, including a bicycle once ridden by Joe Clark, a colourful kite featured in a film about South Africa, and a white ribbon used to alert troops in World War Two to the surrender of a village.
The final comma improves readability in cases like this.
So, sometimes the final comma is needed. Other times you can use it or not. The most important thing is to keep your use consistent throughout your document. So if you use the final comma in a short list once, use it every time. Or if you plan to leave it out of a short list, make sure you leave it out every time. You can make an exception and plop a comma in there, though, whenever it improves readability or is needed to shape the meaning.