What Is the Serial (Oxford) Comma, and Why Do People Care About It?

Perhaps you’ve heard about the serial (or Oxford) comma, and if you have, it might have come with intense opinion. I can’t think of a grammar topic accompanied by so much insistence that the other side is wrong. People like what they like, and when it comes to a serial comma, they’re not going to have their minds changed! So what exactly is it, and why do people care so much? I can’t necessarily answer the latter, but I’ve got you covered on the former.

---

I’m looking for a pediatric board review Qbank with well-written questions, an easy-to-use app, and a search function.

See that comma after “app”? That’s a serial comma—it comes before the final item in a list of three or more things (also known as a series—get it? Series = serial comma). It’s also called the Oxford comma because it was included in the Oxford University Press’s style guide. 

But is a comma there entirely necessary? Couldn’t you still understand the sentence without it?

When I study for the shelf exam, I do three things: learn the material, practice with a Qbank and continually review.

You understood the three study phases mentioned here, right? Of course. That’s because the serial comma is a style choice rather than a grammatical necessity (most of the time). Many style guides recommend using the serial comma at all times for consistency and clarity. However, other guides (such as AP style, which is standard in journalism) only recommend the serial comma when it’s needed for clarity. Otherwise, it’s seen as an unnecessary punctuation mark that takes up space on the page.

What’s an example of a sentence that AP style might recommend using the serial comma?

I’d like to thank my parents, Dr. Peter Rosen and Malala Yousafzai.

Without the serial comma, there’s a chance a reader could misinterpret the writer’s parents as Dr. Peter Rosen and Malala Yousafzai. With the comma, it’s clear that the writer is thanking more than just their parents—they’re also thanking the father of emergency medicine and a human rights activist (perhaps for being inspirations in the writer’s life).

I’d like to thank my parents, Dr. Peter Rosen, and Malala Yousafzai.

---

If you’re deciding whether to include the serial comma in your project or style guide, maybe our reasoning will help. Rosh Review’s standard style is to always use the serial comma. It keeps sentences clear and consistent, and it means the copy editing team doesn’t constantly debate whether a comma is needed in a given list. The team already has near-daily discussions about grammatical nuances, so this is one less thing to talk about!

Here’s the kind of sentence we might discuss if we didn’t have a serial comma rule:

This diagnosis is also used for patients with hypertensive values who have evidence of end-organ dysfunction as manifested by new-onset cerebral or visual disturbances, severe and persistent right upper quadrant or epigastric abdominal pain, thrombocytopenia, progressive kidney insufficiency or pulmonary edema.

Without the comma after “progressive kidney insufficiency,” a reader might stumble over “progressive”—does it refer to both the kidney insufficiency and the pulmonary edema? If so, is a final condition missing from the list? With a serial comma added, there’s no ambiguity.

…new-onset cerebral or visual disturbances, severe and persistent right upper quadrant or epigastric abdominal pain, thrombocytopenia, progressive kidney insufficiency, or pulmonary edema.

---

In the past, I admit I was in the camp of “the serial comma is the only logical option,” but the longer I’ve edited, the longer I see this topic for what it truly is: a style choice. There’s no right or wrong answer as long as you’re consistent. Once a style is chosen for a project—whether it’s a website, a novel, or a Qbank—stay consistent (and keep track of your decisions)! This is why style guides exist: so we don’t have to constantly remember which grammar and style choices have been made over the years.