About Oxford

The Oxford comma, also known as the serial comma, is the comma that precedes a conjunction–usually “and” or “or”– in a series of entities that are separated by commas:

Me, myself, and I
Here, there, and everywhere
Ifs, ands, or buts

There are two schools of thought regarding the serial comma. Those who support its usage claim that it eliminates ambiguity. Those who oppose it usually purport that the conjunction is sufficient to demarcate the final entity in a series.

About Oxford

Depending on which school of thought you belong to, you would write one of the following:

We saw tigers, lions and bears at the zoo.
We saw tigers, lions, and bears at the zoo.

Both sentences are clear because they tell the reader that we saw three types of animals at the zoo. So far, so good–in sentences where the items in a series are simple, the serial comma makes little difference to our understanding. But we should strive for not just clarity, but consistency, when we write. Do more complex sentences remain clear if the serial comma is not used?

According to my teachers in elementary school and high school, the answer to that question is yes–they didn’t teach us to use the serial comma. It was not until I was in first-year university that I learned about the value of using it. (Thank you, Professor Whitla!)

Using the serial comma to resolve ambiguity

Professor Whitla taught his class that the serial comma indicates equivalency amongst the entities in a series. For example, in the sentence below,

is set off as one entity. But what are the others? Are the last three items considered one unit [coffee and green eggs and ham]?

For breakfast, I had toast, coffee and green eggs and ham.

Adding the serial comma shows my breakfast consisted of equivalent items [toast] [coffee] [green eggs and ham]:

For breakfast, I had toast, coffee, and green eggs and ham.

Here’s another illustration of ambiguity in this corny kids’ joke from my childhood:

“What’s red, white and black and blue all over?”
“What’s red, white, and black and blue all over?”

Consider how the serial comma in the second sentence sets off the qualities [red] [white] [black and blue all over], whereas the first sentence might make you think that the object in question is [red]

[blue all over].

(Incidentally, I don’t remember the punchline, but I know it’s corny because all the jokes I knew as a kid were that way.)

Appositives and the serial comma

One way in which the serial comma can actually create ambiguity is how it may seem to create an appositive where none is intended. Consider the following sentence:

The baby likes to play with Elmo, her doll, and blocks.

You can interpret this as saying that the baby likes to play with three toys [Elmo] [her doll] [blocks] or two toys [Elmo, her doll] [blocks]. Without the serial comma, the sentence would imply that she plays with three toys, since appositives must be contained within commas unless they are at the end of a sentence.

To resolve the ambiguity, you can rewrite the sentence by changing the order of entities in the series:

The baby likes to play with blocks and Elmo, her doll. (two toys)
The baby likes to play with blocks and her doll Elmo. (two toys)
The baby likes to play with blocks, Elmo, and her doll. (three toys)

Last words on the serial comma

Whether or not you use the serial comma, remember to be consistent. As long as you stick to one method, readers should be able to glean your meaning. And if you find that a sentence just isn’t working, it may just be best to rearrange it–a practice that would have benefited The New York Times (who uses AP style, which does not support the serial comma) in this case:

The Times once published an unintentionally humorous description of a Peter Ustinov documentary, noting that “highlights of his global tour include encounters with Nelson Mandela, an 800-year-old demigod and a dildo collector.” This would still be ambiguous if a serial comma were added, as Mandela could then be mistaken for a demigod, although he would be precluded from being a dildo collector. (Source: wikipedia)
Adding the serial comma so that the sentence reads “highlights of his global tour include encounters with Nelson Mandela, an 800-year-old demigod, and a dildo collector” might still be ambiguous because “an 800-year-old demigod” can be read as an appositive for Nelson Mandela.

Lesson learned: It’s good to proofread!