What the hell is an appositive?
We’ve all seen sentences like these:
Mike and his wife, Jill, took the scenic route on their way to dinner.
Harry and his friend Lou went out for drinks.
Have you ever wondered why the name Jill is separated by commas in the first sentence, but Lou isn’t?
Grammatically speaking, the name Jill in the first sentence is a nonrestrictive appositive and is therefore set off from the noun with commas. The name Lou in the second sentence is a restrictive appositive and shouldn’t be set off with commas.
But, wait… Hold the phone. What the hell is an appositive?
If you’re like me, the first time someone said the word appositive to you, your head tipped to the side and you made that little sound puppies make when they’re confused.
An appositive is simply a big name for a noun or noun phrase that sits next to a noun and helps identify or define it. Most often we see appositives after the noun they identify, as in the sentences above where both Jill and Lou are appositives, but they can come before the noun, too.
So now that we understand what an appositive is, we can address the comma confusion. Nonrestrictive appositives are set off with commas because they offer additional—not essential—information about the noun and can be removed from the sentence without changing the meaning of the noun or creating confusion.
Back to our first example. We can assume that since polygamy is predominantly frowned upon, Mike only has one wife—Jill. Removing her name from the sentence doesn’t affect the meaning:
Mike and his wife took the scenic route on their way to dinner.
Conversely, restrictive appositives supply essential information about the identity or definition of the nouns they refer to and are not set off with commas because they cannot be removed without altering the noun’s meaning or creating confusion.
In our second example, we have no idea how many friends Harry has, but we can assume it’s more than one. So if we remove the name Lou, we’re left with:
Harry and his friend went out for drinks.
Raise your hand if your knee-jerk reaction to reading that sentence is “Which friend?” That’s why the appositive is restrictive in this case. It supplies essential information about the noun.
And if you’re like me and use little tricks to help you remember things, the rule about appositives and commas can be generalized that nonrestrictive appositives give additional information, therefore you add commas. Restrictive appositives give essential, not additional information, therefore… you don’t add commas.