Fueling one of the more popular English language debates are the two most commonly used style guides: the The Chicago Manual of Style and the AP Stylebook. The guides have opposite rules for using the serial comma (that last comma before the conjunction), with Chicago supporting the inclusion of the serial comma and AP omitting it.
Specifically, AP uses commas to separate elements in a series but does not include the serial comma in a simple series: I like cake, ice cream and pie.
That’s what most people understand. What’s less understood is that AP has exceptions, which are meant to help the reader understand the series. We are to use the serial comma:
- In a complex series. In other words, the items are long, as with a series of independent clauses, or already have punctuation in them. Here’s an example from the stylebook: The main points to consider are whether the athletes are skillful enough to compete, whether they have the stamina to endure the training, and whether they have the proper mental attitude. Given the length of each item in the series (whether the athletes are skillful enough to compete), the serial comma lets readers know the last item in the series is coming up.
- When one of the items in the series already has a conjunction. The serial comma tells readers which items are grouped together, as with this AP example: I had orange juice, toast, and ham and eggs for breakfast. Without the serial comma, ham and eggs could be one item or two. When such a question would change the meaning of the sentence, AP wants us to use the serial comma.
As to why the rule is so misunderstood, I think it’s just how humans are wired. We look for shortcuts to make our work easier, and it’s easy to memorize “don’t use the serial comma.” It’s harder to remember the exceptions, and we often forget them. And if the writers and editors using the stylebook don’t look up the rule, they won’t be reminded of the exceptions. This is especially understandable when you’re as overworked as so many journalists are.
A version of this article originally published in 2013 in Copyediting newsletter.