Grammatically speaking, “appositive” is a fancy word for “equivalent.” For example, when we refer to your dog Smurf, “Smurf” and “your dog” are appositives—the same thing (or animal, in this case) restated in different words.
And we know that Smurf can’t be your only dog, because the name isn’t preceded by a comma. Add one—“your dog, Smurf”—and it’s now clear that you have just the one dog.
Or is it?
Meaning isn’t determined by commas alone; it also depends on context. Moreover, of the two, context is usually the more important consideration; commas merely work in support of context. And that means commas aren’t always strictly necessary, even when you think they might be.
Sometimes commas signal pauses. But in formal prose—or any carefully edited prose, for that matter—logic, not pacing, is the primary consideration.
Here’s how that logic is supposed to work with appositives (see also CMOS 5.23 and 6.28). Let’s return to your pet dog. For the sake of the examples, we’ll pretend your dog is a she. (If you’re not a dog person, substitute “cat” or “frog” for “dog.”)
I have a dog. Her name is Smurf. She’s cute.
These three sentences can be combined into one, with or without the help of commas:
My dog, Smurf, is cute. [Smurf is your only dog.]
My dog Smurf is cute. [You have other dogs.]
The commas in the first example work much like parentheses. They introduce the name “Smurf” as something extra. It’s extra because if you don’t have any other dogs, “my dog” tells us which dog is cute.
But in the second example, the absence of commas suggests there are other dogs. You are referring to your dog Smurf as opposed to, say, your dog Spot. In the case of more than one dog, the name identifies which one; therefore, it should not be set off by commas.
Now let’s switch things around. As we learned at the beginning of this post, nouns placed in apposition to each other are equivalents, which means they’re interchangeable. And when you switch the order, putting the name first, things get interesting:
Smurf, my dog, is cute.
Smurf my dog is cute.*
That’s right—commas are usually required in this version of the sentence, no matter how many dogs you have, and no matter how many commas you normally like to use. That’s because when the name comes first, we know who is cute: Smurf.†
Names Restrict Meaning
Writers use words to assign meaning to people, places, ideas, and actions. To restrict the meaning of something is to narrow it down to one thing.
There are lots of pets with the name Smurf. But given enough context, a name—specifically, a proper noun given to a particular person or other entity—is usually sufficient to allow readers to make a positive identification. Once we know that we’re referring to Smurf, and specifically to your Smurf, the mystery is gone.
That’s assuming there was any mystery about your dog to begin with, or that we need to know about your other dogs, if you have any.
Context before Commas
Context is the environment in which words live and to which they ultimately refer. In most prose, this environment is the real world. In fiction, it could be a version of the real world, or some other world invented from the ground up.
Context also includes, more immediately, the words on the page.
Let’s return to Smurf. And let’s say we learn from context that you—the first-person narrator in a book about your dog—had one dog in the 1980s. That dog’s name was Smurf:
Back then I was living alone in a trailer. Alone except for a little dog. A little dog and a portable TV. My dog, Smurf, was so cute.
Most editors would keep those commas. Thanks to the established context, “my dog” is as good as a name. Which dog? The one that was living with you in a trailer. And as we’ve seen, when we know the identity of the first noun, a comma is normally required before the second noun (paired with an additional comma if the sentence continues).
But are commas always necessary in cases like this?
Commas with appositives are sometimes known as “spousal” commas. That’s because marriages tend to be monogamous. Simply by saying “my spouse” (or “my husband” or “my wife”), you’ve already identified the person. You can only have one, right?
According to that logic, and regardless of context, you’re supposed to write “my husband, Sam” (with one or two commas), not “my husband Sam”—and, strictly speaking, you have to do this each time Sam is mentioned in that way. By the same token, if you have only one sister, you’re supposed to write “my sister, Samantha”; if you have more than one sister, the comma is omitted: “my sister Samantha.”
But what if you were married before, or might marry again? And can we always be sure how many siblings someone has? What if we’re talking about a friend rather than a family member? A better question might be this: Does it matter to the reader how many wives you have, or siblings, or friends—or dogs?
It might, but it shouldn’t come down to commas alone.
The Verdict: If Commas Feel Like Overkill, Omit
It’s an editor’s job to help writers by keeping track of every last detail, including how many dogs you have, and when you had them—and whether this marriage is a second one (or a fourth) and how many siblings and friends are in the picture. When one of these is ambiguous, an editor may suggest a clarification (or ask the author to provide one).
Commas, or their absence, are one of the tools that can be used toward achieving this end. But if a reader can’t be sure from context, commas are unlikely to help.
And they can feel like overkill.
As we’ve seen, when a name comes first, commas are usually required (“Smurf, my dog, is cute”). But when the generic term goes first—whether it’s a spouse, a pet, a sibling, or a friend—commas play a lesser role. In fact, they can often be omitted, even when “the rules” might suggest otherwise.
If it starts to feel heavy-handed to use commas each time—especially if the tone is less than formal—go ahead and write “my husband Sam” or “my dog Smurf,” even if Sam is the only husband and Smurf the only dog:
My husband Sam knew that he was taking a risk when he married me.
My dog Smurf is an only dog, but I also have cats.
My first husband, Sam, knew that he was taking a risk when he married me.
In sum, when the generic term comes first, it may require additional context before the reader knows its identity. Sometimes that context is an adjective (like the word “first” in that final example); in other cases it consists of a more elaborate explanation (as in the earlier example featuring the trailer). In either case, if a name then follows the generic term, it is usually set off by commas.
In the absence of such context, however, commas become optional—particularly whenever the existence of other spouses or dogs or siblings is beside the point, as it often is.
* This sentence can be punctuated in two ways. To tell someone your dog is cute, use two commas (as in the first example). But to tell someone named Smurf that your dog is cute, use one: “Smurf, my dog is cute.” (For more on commas with direct address, also called vocative commas, see CMOS 6.53.)
† There are exceptions, usually when a name could apply to more than one entity. For example, you might need to refer to “Smurf the dog” as opposed to “Smurf the cat” (no commas).
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