An appositive is a noun or noun phrase placed right beside another noun to rename it: “My aunt, a pilot, flew us home.” It works like a predicate noun that needs no verb, and like a modifier it sits next to the word it tells about.
Key idea
Commas depend on whether the appositive is needed to tell which one. If it only adds information, set it off with commas. If it identifies which one, use no commas.
Why it works
Commas tell the reader “this is extra.” “My brother, Leo, plays chess” says you have one brother and adds his name. “My brother Leo plays chess” uses the name to pick out which brother, so it suggests you have more than one.
Worked example: Commas or not?
Ana has two brothers. Punctuate: “Ana’s brother Leo plays chess.”
- She has two brothers, so Leo tells which one.
- An appositive that tells which one is needed: no commas.
Answer: “Ana’s brother Leo plays chess.”
Worked example: A longer appositive
Find the appositive: “We read Charlotte’s Web, a book about a pig and a spider.”
- a book about a pig and a spider renames Charlotte’s Web.
- It adds information (there is only one Charlotte’s Web), so a comma sets it off.
Answer: a book about a pig and a spider
Common mistake
Leaving out the commas around an appositive that only adds information, or adding commas around one that tells which person or thing is meant (“my friend, Ana,” when you have many friends). Ask: without it, would the reader know which one?