The decision whether to use the Oxford comma, also known as the serial comma, divides many people. Technically, both choices are correct—so long as you use one style consistently, of course.
I’m not here to argue how one of these punctuation choices is right while the other is wrong. Instead, I’d like to call to your attention to the fact that by not using this handy device, you are removing one tool from your belt, and as a writer, it’s beneficial to have every device at your disposal.
First, let’s define our term of the day. The Oxford English Dictionary says this:
Oxford comma n. [after the preferred use of such a comma to avoid ambiguity in the house style of Oxford University Press] a comma immediately preceding the conjunction in a list of items.
I met with x, y, and z.
I met with my teachers, Mom, and Dad.
You are separating three individuals with a comma (i.e. teachers + Mom + Dad). The Oxford comma is the the final punctuation before the conjunction and.
The purpose of this device is the primary use defined above, to avoid ambiguity. If the comma is not used, this is the resulting sentence:
I met with x, y and z.
I met with my teachers, Mom and Dad.
By not using the Oxford comma, the sentence has changed by identifying my teachers as Mom and Dad (i.e. teachers = Mom + Dad) rather than listing three separate persons. If I meant to convey the first example (teachers + Mom + Dad), then I have introduced ambiguity and miscommunicated my intent.
That’s the basic premise. Now I’m going to show you why you want every tool at your disposal.
Take these two examples:
I invited Susan, Jim and Kelly, and Patrick.
I invited Susan, Jim and Kelly and Patrick.
Sentence one showcases a natural pattern of speech. When two people are in a relationship, we often group their names together as if to say they are one entity, or simply a unified pair. The first sentence conveys that Susan and Patrick are unrelated individuals while Jim and Kelly are to be classified together.
If you chose to not use the Oxford comma, as seen in example two, the sentence looks overly complex and assumes a run-on feeling. There are too many unseparated conjunctions as if a child were telling the story: “And this happened and this happened and that happened.” By not using the comma before the final conjunction, you have disqualified a useful piece of writing—that is, the ability to group items in the middle of a sentence in a clear fashion.
Another tool that benefits from the clear distinction of the Oxford comma is the following sentence from my post on epigraphs:
The book was about friendship, loyal and otherwise.
I use this device all the time.
If I did not employ the Oxford comma, the sentence could appear to be an “x, y and z” compound predicate, which it is not. The reader would be distracted until he determines what is actually occurring on the page.
Since I employ the Oxford comma, there is no confusion. “X, y and z” does not exist in my writing. Therefore, “loyal and otherwise” can properly act as adjectives modifying “friendship” without any conflicts of identical form.
Now, let’s say a particular work does not use the Oxford comma.
If you chose to use the comma for this one sentence, you would eliminate the ambiguity, but then you would be changing writing styles halfway through the piece, which is a big no-no. Of course, you could easily write the sentence “I invited Susan, Jim, Kelly, and Patrick,” but then you couldn’t disclose that Jim and Kelly are an item as you would like, the same way “I’m serving chicken, carrots and peas, and biscuits” shows that carrots and peas are combined as a single dish.
See the predicament?
As a craftsman, I want as many tools at my disposal at possible, especially the perfect one for a given situation when a substitute just won’t suffice. If you’re a true believer of not using the Oxford comma, by all means, continue writing your way. You’re just missing out.