Commas are a workhorse punctuation mark. They’re like the people you ride with on the subway every day, the delivery guy who comes by your office, and the parents of your children’s classmates — you see them so often that you think you know them just from sheer exposure. Rarely does a paragraph go by in which you don’t encounter a comma. But like those familiar strangers, commas are complex. You might get a sense of them from casual observation, but to truly know them, you have to dig deeper.

Let’s get to know the comma a little better.

The Oxford comma

Sometimes your subway buddy wears a suit with leather Oxfords and sometimes he wears jeans with Converse high-tops. His different activities call for different styles. So it is with the comma.

If you’re writing a nonfiction book, you need a tight-laced style: the Oxford comma. It’s orderly. It’s clear. Whoever told you the and takes the place of the comma was wrong.

The Oxford comma (the style recommended by Oxford University Press and Chicago Manual of Style) is the last comma in a series, the comma before the final “and” or “or”:

He wore a suit, a tie, and Oxfords.

He felt hot, sweaty, and tired.

If you’re writing something lighter — a press release or newspaper articles — you can get away with a more relaxed style: omit the Oxford comma. The Associated Press recommends against the Oxford comma, unless leaving it out will cause confusion.

He wore jeans, a T-shirt and high-tops.

He felt relaxed, cool and eager.

When might the Oxford comma be needed for clarity? Ponder the difference between these two examples:

We invited the jugglers, JFK, and Stalin.

We invited the jugglers, JFK and Stalin. 

Commas that separate an appositive

Let’s let JFK and Stalin, those wild and crazy jugglers, lead us to appositives, which are the reason the second JFK-Stalin sentence is misleading without an Oxford comma.

Appositives are nouns or noun phrases that name the nouns or noun phrases they follow, and appositives follow a comma if deleting the appositive wouldn’t change the big-picture meaning of the sentence. Here are two examples:

She had a crush on the guy from the subway, Xavier. 

“Xavier” is the appositive that tells us the name of the guy from the subway. We can also flip it around:

She had a crush on Xavier, the guy from the subway. 

Now “the guy from the subway” is the appositive that tells us who Xavier is.

When a list includes a mix of descriptions (e.g., jugglers) and names (e.g., JFK and Stalin), it can look like the last two items are appositives instead of independent items in the list:

We invited two dead political figures, JFK and Stalin. (clearly an appositive)

We invited the jugglers, JFK and Stalin. (meant to be a list without an Oxford comma, but easily misinterpreted as an appositive)

Commas around nonrestrictive phrases

In the sentence “We invited two dead political figures, JFK and Stalin,” the meaning of the sentence doesn’t change if we leave off “JFK and Stalin.” We have less information, but what’s happening isn’t different. That’s why there’s a comma before “JFK and Stalin” — they’re nonessential.

If leaving out the appositive would change the meaning of the sentence, it isn’t separated from the rest of the sentence by commas. Consider these examples:

Xavier’s subway buddy, Shawna, always sits to his right.

In this sentence, Shawna is Xavier’s only subway buddy, so her name is extra information and is isolated by commas. If we take out the commas, we change the meaning:

Xavier’s subway buddy Shawna always sits to his right. [no commas]

In this sentence, Xavier has many subway buddies and we’re being told that it is just one of those buddies, Shawna, who sits to his right. If we leave out “Shawna” and write “Xavier’s subway buddy always sits to his right,” we would presume that Xavier has only one subway buddy and we don’t know his or her name. Leaving out “Shawna” would change the meaning of the sentences, which makes it essential, and means that it is not isolated by commas. (These essential elements are also called “restrictive” because they restrict the meaning of the sentence.)

Isolating nonessential elements is one of the big jobs of a comma; it extends far beyond appositives. Think of the comma as that unapproachable person on the subway who gives you a “you don’t need to know that” look when you ask a friendly question. Commas around a phrase are a clue that you don’t need to know the information; it can be lifted out of the sentence without changing the meaning. Consider these examples:

People, who talk on the subway, annoy Isabella.

In this sentence, Isabella finds all people annoying. It’s just extra information that their talking on the subway is one of the things that gets under her skin.

People who talk on the subway annoy Isabella. [no commas]

In the second sentence, Isabella is less of a misanthrope. She’s only annoyed by people who talk on the subway, not all people.

Summary

Commas have many other uses, but you’ve started to get to know them a little better. Remember that the Oxford comma is a style choice and sometimes you need it to avoid confusion. Further, commas often surround elements that are merely extra information and not essential for the meaning of the sentence.

A version of this article originally appeared in Office Pro Magazine.

Image courtesy of Shutterstock.