Try reading each of these lists to yourself:
“Red, white, and blue.”
“Red, white and blue.”
Which was easier to understand?
Chances are, you didn’t have much trouble with either of them. Both lists are grammatically correct, and both lists have the same meaning.
The only difference between the two is the comma appearing between the words “white” and “and” in the first list.
This final comma is called an Oxford or serial comma, and despite its relatively small grammatical role, it has been the subject of many heated debates.
Some style guides recommend it, others shun it, and many writers have strong opinions about which side is correct.
The truth is that the Oxford comma’s usefulness depends entirely on its context.
How the Oxford Comma Reduces Ambiguity
Supporters of the Oxford comma argue that it helps reduce ambiguity. This is often true.
For example, take the following sentence: “Joe went to the store with his parents, Superman and Wonder Woman.”
As written, the sentence’s meaning is unclear. Did Joe go to the store with his parents and Superman and Wonder Woman? Or did Joe go to the store with his parents, who are Superman and Wonder Woman?
Proponents of the Oxford comma point out that it would clear up this confusion.
By placing a comma after Superman, the sentence reads: “Joe went to the store with his parents, Superman, and Wonder Woman.”
It’s now clear that Superman and Wonder Woman are not Joe’s parents. In this case, the Oxford comma has helped remove ambiguity.
How the Oxford Comma Introduces Ambiguity
Unfortunately for the Oxford comma’s advocates, examples like the one above only tell half the story. In other cases, the Oxford comma can actually create ambiguity.
Let’s take a look at a similar sentence, but with one crucial difference: “Joe went to the store with his father, Superman and Wonder Woman.”
This sentence has no Oxford comma, and yet it’s meaning is completely clear. Joe went to the store with his father and Superman and Wonder Woman. Since “father” is a singular noun, it couldn’t possibly refer to “Superman and Wonder Woman” (unlike the plural noun “parents” in our previous example).
When we add an Oxford comma, we actually end up with a more ambiguous meaning: “Joe went to the store with his father, Superman, and Wonder Woman.”
Now it reads as if Joe’s father might be Superman. The Oxford comma has introduced exactly the type of ambiguity that it helped remove in the original example!
In this case, whether the Oxford comma creates or removes ambiguity depends entirely on whether the first item in the list is plural or singular.
Should You Use Oxford Commas?
We’ve seen how an Oxford comma can resolve ambiguity in some cases, but create it in others. In most cases, it won’t make any difference at all.
So, what’s the bottom line? Should you use Oxford commas?
The answer is that it depends on what and for whom you’re writing.
Like many aspects of grammar, there isn’t a universal, always-applicable rule. In the United States, for example, academic writing tends to include Oxford commas, while periodical writing tends to exclude them.
When it comes to Oxford commas (and grammar in general), the best practice is to consult the style guide which is most applicable to the type of writing you’re doing.
If you’re writing for a research paper, follow the MLA handbook (or whichever guide is assigned by your professor). If you’re writing an op-ed, follow the AP stylebook.
When you aren’t sure which style guide is appropriate, simply reach out to the person editing or grading your work.
As far as ambiguities go, there’s a better way to clear them up than relying on the presence or absence of a single comma. Instead, restructure your sentence so that its meaning is clear regardless of whether a serial comma is used.
Our first example could be reworded as: “Joe went to the store with Superman, Wonder Woman, and his parents.” By simply rearranging the order of the list, we’ve removed the ambiguity.
Now the meaning no longer hinges over the placement of a single comma. Readers will have an easier time quickly parsing the sentence, regardless of whether an Oxford comma is used or not.