Dave, an 8^th grader, asks:

Let's say you are making a list. Would you, or would you not put a comma before the “and”?

Good question. What Dave is referring to here is the Oxford comma, sometimes also called the “serial comma.” We know that we should put a comma between each item in a list to avoid confusion, but there is some debate over whether there should be a comma after the second-to-last item.

For example:

“Today we went to the store and bought milk, bread, eggs, and apples.”

The comma after the word “eggs” is an example of the Oxford comma. Some say that this is unnecessary, because the word “and” indicates the almost-end of the list and serves the same function as a comma.

Those opposed to the Oxford comma would write that sentence this way:

“Today we went to the store and bought milk, bread, eggs and apples.”

Now, the addition of an Oxford comma may not seem like a big deal in a short sentence like this. But the longer the sentence gets, the more useful it can be. And I don’t mean “longer” in the sense of more items in the list, but more complex “items,” such as phrases rather than single words.

For example:

“When interviewing potential new employees, Richard was careful to pay attention to each candidate’s sense of confidence in their abilities, attitude toward their previous education and employment and their ability to express themselves in a succinct manner.”

That’s a pretty long sentence, and each item is much longer than in our previous sentences. Do you see how the section “education and employment and their ability” could be confusing upon first reading? Without the Oxford comma here, that last segment is a lot longer and starts to feel like a run-on sentence.

 Let’s look at this sentence again with the Oxford comma:

“When interviewing potential new employees, Richard was careful to pay attention to each candidate’s sense of confidence in their abilities, attitude toward their previous education and employment, and their ability to express themselves in a succinct manner.”

By using the Oxford comma, we help to avoid confusion about whether the word “and” is being used as a part of one of the list items, or indicating the last item of the list.

Those who recommend the use of the Oxford comma will also use sentences similar to the following one, as an example for why we need that extra comma:

“I’m grateful to my sisters, Jan and Devon.”

What is the speaker saying here? Are they grateful for their two sisters who are named Jan and Devon, or are they grateful to their sisters and two other people named Jan and Devon? In other words, does the comma introduce the first item in a list, or does it introduce an elaboration upon that first item?

So that's an explanation of the Oxford comma.

But that’s not what this question is asking. The question is asking whether the Oxford comma should be used in general.

Well, first I’ll tell you what a couple style guides recommend.

The Chicago Manual of Style says the following:

“When a conjunction joins the last two elements in a series of three or more, a comma—known as the serial or series comma or the Oxford comma—should appear before the conjunction. Chicago strongly recommends this widely practiced usage … since it prevents ambiguity.” (6.18)

The AP Stylebook, on the other hand, says to omit the Oxford comma in a simple series, but recommends it for a longer, more complex series (like the second pair of sentence examples above).

Personally, I use the Oxford comma even in a simple series, following Chicago’s recommendation. For one thing, consistency is important, and rather than trying to determine how “complex” a complex sentence must be before it merits a serial comma, I think it’s best to use it in every series. When we are able to expect the Oxford comma to be used, we don’t have to wonder while reading whether an “and” is a conclusion of a series or part of a series element. (For example, “For breakfast we had eggs, bacon, toast and jam.” One might expect “toast and jam” to be a combined element, and so without the Oxford comma, you have to finish the sentence before you figure out what the “and” is doing.)

The role of punctuation is to make our words easy to understand, and having the consistent structure of an Oxford comma in place aids in understanding. The more consistent we can be with punctuation, the more attention we can focus on the words themselves, and the more quickly and easily we’ll be able to read and understand another’s writing.