Essential and Nonessential Sentence Elements
Ah, the comma. I’d argue that it’s the trickiest punctuation mark to master for two reasons: it has so many different functions that it can be overwhelming to remember them all, and the rules that govern its use are subjective at best. Some writers love commas and sprinkle them everywhere, sometimes in places they don’t belong. Others find them intrusive and stay away from them if at all possible, even at the cost of clarity. Regardless of where you stand in the great comma debate, there’s little doubt that the comma serves a variety of important purposes. One of the most common comma-related edits I make is related to whether an element in a sentence is essential or nonessential.
Essential and nonessential elements
An essential element (also called restrictive) is a word or phrase that contains required information the reader must know in order to fully understand the sentence. If you remove the essential element, the meaning of the sentence may change or be ambiguous. A nonessential element (nonrestrictive) is the opposite. It adds information that isn’t necessary in understanding the sentence, and removing it will leave the meaning unchanged. These are also referred to as essential/nonessential modifiers or clauses.
I find the easiest way to illustrate the difference is with names. Since I love Parks and Recreation, let’s use the characters as an example.
Essential element:
Never talk to or look at April’s friend Orin.
No one understands how their coworker Jerry is married to such a beautiful woman.
Nonessential element:
The Parks and Rec director, Ron, hates Canada, skim milk, and Ron Dunn.
Chris sees his therapist, Dr. Richard Nygard, fifteen times a week.
So what’s the difference between these sentences, and what makes some information essential and some nonessential? In these examples, it’s all about whether it’s necessary to name the character being referred to or whether the sentence will still make sense without the name(s). In the first two sentences, these elements are essential. April (likely) has more than one friend, so specifying Orin is necessary. The Parks department has many employees, so the coworker has to be named in order to know which one is being discussed. In the other two sentences, these elements are nonessential. The Parks department has only one director, so adding Ron’s name is a nice but unnecessary detail for the sentence to make sense. Removing Dr. Richard Nygard’s name from the last sentence doesn’t change the meaning because the reader will still know exactly who’s being referred to—Chris’s only therapist.
Even though these examples all use names as the essential or nonessential elements, it’s important to know that any detail can be used in this way, such as titles or descriptions, as shown later.
Punctuating with commas
The way to tell the reader that an element is essential or nonessential is with the presence or absence of commas. If an element is essential to the sentence, no commas are used. If an element is nonessential, commas surround it. Think of this pair of commas like parentheses, waving to the reader in a “this information is good to have but you don’t technically need it” type of way. You can pluck out whatever is contained in the commas without consequence. Like parentheses, too, there must be an opening and closing mark. If the nonessential element is at the end of the sentence, you only need the one before it. These commas are sometimes called “only” commas because they are used when only one thing can be referred to (one person, one type, one item), thus rendering the specifier within the commas nonessential.
How does the presence or absence of commas change the meaning of the following sentences?
The Roomba with the MP3 player on top dresses up as a ghost for Halloween.
The Roomba, with the MP3 player on top, dresses up as a ghost for Halloween.
The first sentence implies that there are many Roombas in question, but the one with the MP3 player on it is the one that dresses up as a ghost. In the second sentence, there are commas around “with the MP3 player on top,” which indicates it’s nonessential to the sentence and an additional descriptor. Therefore, a reader would think there’s only one Roomba, which dresses up as a ghost, and it also has an MP3 player.
Andy stars in the show titled The Johnny Karate Super Awesome Musical Explosion Show.
Andy stars in the show, titled The Johnny Karate Super Awesome Musical Explosion Show.
In this example, the first sentence means multiple shows exist, and Andy stars in this specific one. The second sentence implies he stars in the one show being referred to in this context, which is called The Johnny Karate Super Awesome Musical Explosion Show.
“That” vs. “which”
In US English, the uses of “that” and “which” are fairly rigid. “That” is used with essential/restrictive elements, while “which” is used with nonessential/nonrestrictive elements. When using “which,” commas are again placed around the nonessential element.
Correct: The diner that serves waffles is Leslie’s favorite restaurant.
Correct: The diner, which serves waffles, is Leslie’s favorite restaurant.
Often considered incorrect in US English: The diner which serves waffles is Leslie’s favorite restaurant.
In the first example, there are many diners, but the one that serves waffles is Leslie’s favorite (clearly JJ’s). Removing the detail about waffles changes the meaning because it’s the only way to distinguish her favorite restaurant from all the others. Therefore, this clause is essential and should use “that.” In the second example, her favorite restaurant is the one diner around, and it also happens to serve waffles. Removing the detail about waffles doesn’t change the fact that the diner is her favorite. Therefore, this clause is nonessential and should use “which” with commas around it. In the third example, “which” is used in the sense of “that” in the first sentence and doesn’t have commas around it. This last type of sentence construction is seen often in British English but would likely be changed in US English, though not all works written in US English stick to this either.
Final thoughts
Sometimes the best way to determine whether an element is essential or nonessential is to test it out. Write the sentence, then remove the part in question. Does the meaning of the sentence change without it, or does it stay the same? Is the meaning now ambiguous or unclear, or will the reader still know what’s being referred to? The answers to these questions will help you decide whether it’s essential or nonessential and how you may need to punctuate it. In my writing group, I’m the person who asks the writer whether the character has only one brother or if there’s more than one, which affects whether the commas around the brother’s name should exist or not. Even though this may seem like a trivial detail, it can make all the difference in meaning.
