First off, what is an appositive?
An appositive is a noun or pronoun (usually with modifiers) that is next to another noun or pronoun in order to explain or identify.
Example: Your friend Colleen is in the library.
Friend is the noun and the the appositive is Colleen.
Appositives usually follow the word it explains or identifies, but sometimes it come before the word it is explaining or identifying.
Example: The chief surgeon, an expert in organ-transplant operations, took the interns on a tour of the hospital.
an expert in organ-transplant operations =appositive
Example: My beautiful corgi, Cooper is my favorite pet.
my beautiful corgi=appositive
If the appositive is essential to the sentence, then the appositive does not need to be off set with commas. However, if the sentence would make sense without the appositive, then commas are needed.
Example: My son, the doctor, will be visiting next week.
The sentence would make sense if it read: My son will be visiting next week. Commas need to be placed before and after the appositive the doctor.
Example: 60 Minutes, the TV news magazine program, featured a story on the popular singer, Whitney Houston.
In this example, a comma is placed before and after the appositive the TV news magazine program. A comma is also placed after popular singer. The reason the commas are needed is because the sentence would make sense without those appositives. The sentence without the appositives would read: 60 Minutes featured a story on Whitney Houston.
Example: The actor Paul Newman directed only one picture.
Commas are not needed in this sentence because the appositive Paul Newman is needed to understand what actor directed only one movie.