Also known as the serial comma, the Oxford comma is the comma placed before the conjunction that precedes the final item in a list of three or more items. Here is an example.
There are lions, tigers, and bears.
I’ve written about the power of the comma before and how the meaning of a sentence can change depending on whether or not you place a comma. In this instance, whether or not you include the comma between “tigers” and “and” really doesn’t affect the overall meaning. But what is correct?
The American flag is red, white and blue. OR
The American flag is red, white, and blue.
Fortunately or unfortunately, the writing community is torn on the issue. The Chicago Manual of Style and the American Medical Association, among others, state that the serial comma should be used when a “a conjunction joins the last two elements in a series.” On the other hand, the AP Stylebook and the New York Times stylebook say that the final serial comma should not be included.
For my part, I find myself using the Oxford comma more often than I choose to leave it out. This is more for clarity and to prevent ambiguity, but it is largely a stylistic thing too. It’s a matter of choice, just like how split infinitives may still get purists to cringe, but they are becoming increasingly acceptable.
In the case of the Oxford comma, there are specific instances where certain rules are to be followed–like if you are adhering to the MLA standard–but for average writers under average circumstances, its inclusion and its omission are both deemed correct.