An appositive is a noun or noun phrase placed beside another noun or noun phrase to identify or explain it. In My only houseplant, a jade plant, survived the move, my only houseplant and a jade plant refer to the same plant.
When an appositive needs commas
Use commas when the reader can already identify the person or thing and the appositive adds a detail. In Alina, my cousin from Boise, arrived early, the name tells us who arrived. The appositive explains the relationship.
When an appositive identifies the noun
Leave the commas out when the appositive helps identify which person or thing you mean. In My cousin Alina arrived early, the name can tell readers which cousin arrived. See noun for the kinds of words that can do this work and comma for more on setting off supplementary information.
