Let me start out by saying this, I am an advocate of the Oxford comma. Yet, not everyone is. Some, in fact, adamantly refuse to use them (varies by style guide ultimately). They argue that it is stylistic, and in most situations, superfluous. I agree with them that it is stylistic punctuation, but I have also learned that it is stylistic punctuation that can often differentiate between good writing and mediocre. How do I figure that? Good writing is crisp and concise, except in those moments where the author wants to us oblique or vague language to add intrigue or doubt for the reader. But those are intentional moment. Ones that are considered, and not just the result of poor writing.
Before I get into it, a little history.
Named for the standards guide utilized by the Oxford University Press, the Oxford comma, also known as the Serial, or Harvard comma, is that seemingly isolated punctuation mark used before the conjugation and the last item in a lists, or series.
Take the following:
"Walter invited the beggars, Father Emilio and Chuck the Butcher", as an example. Without the Oxford comma in this sentence, the reader infers that Walter invited two beggars, and their names were Father Emilio and Chuck the Butcher. This is hardly concise writing, and it raises doubt and confusion in the reader. They question who is invited, and who the beggars are. Now take the same sentence, and use proper grammar: "Walter invited the beggars, Father Emilio, and Chuck the Butcher". Now we understand that Walter invited beggars, the priest, and the butcher. Three separate entities. Ambiguity clarified.
But there is more. "Bring me saltpeter, brown paper and turpentine." There is nothing structurally wrong with the way this sentence is written, but you should consider how the reader will interpret it as it pertains to your story. Without the Oxford comma, the reader may infer that there is some special connection that the second and third items on the list share that they do not with the first. Granted, you will never be able to remove all ambiguity, as much of it is determined by a host of factors, most of which are associated with the reader and out of your control. Yet, with that said, there are instances where Oxford commas may actually confuse the subject, or object of your sentence. It is these situations where it should not be used.
Take this example from the 1934 style book of the New York Herald Tribune: "Those at the ceremony were the commodore, the fleet captain, the donor of the cup, Mr. Smith, and Mr. Jones." (Okrent) Now it may not look strange at first, but when you consider what the writer is trying to say, you begin to see how the Oxford comma between Mr. Smith and Mr. Jones skews the meaning. In this case, Mr. Smith is in fact not the donor of the cup. So this comma actually leads the reader to a false conclusion. Removing the serial comma would clarify it a bit, while rewriting would definitely clear up any further confusion.
In the end, the Oxford comma is a valuable bit of stylistic punctuation, one which can help to reduce ambiguity in writing. But like everything else, its use should be considered carefully. I don't agree with the crowd that outright refuses to use them. But I also don't believe that it should always be used, regardless of application. The truth, as they say, lies somewhere in between. Find that happy balance, or equilibrium, and your writing will surely benefit. Happy scribbling!
Okrent, Arika. "The Best Shots Fired in the Oxford Comma Wars". Mental Floss.com. Language.