Appositive

An appositive is a noun or noun phrase that sits beside another noun and renames or further identifies it. In the sentence "My neighbor, a retired firefighter, waters our plants," the phrase "a retired firefighter" is an appositive renaming "my neighbor." When the appositive includes its own modifiers, the whole unit is called an appositive phrase.

The key punctuation rule turns on whether the appositive is essential to identifying the noun. A nonessential (nonrestrictive) appositive adds extra information and is set off with commas: "Maya Angelou, a celebrated poet, wrote memoirs too." An essential (restrictive) appositive is required to know which person or thing is meant, so it takes no commas: "The poet Maya Angelou wrote memoirs too." A quick test: if you can delete the phrase and the sentence still identifies its subject clearly, use commas.

Appositives also give writers a clean way to combine choppy sentences. Instead of "Mr. Chen is our principal. He canceled the assembly," you can write "Mr. Chen, our principal, canceled the assembly." Dashes or colons can replace commas when the appositive contains internal commas or deserves emphasis.

Appositives are a favorite punctuation target on the ACT English and SAT Writing sections. Expect questions that ask whether an appositive needs commas, whether both commas are present (a comma on only one side is always wrong), and whether a phrase is essential or nonessential.