|Words in nonrestrictive apposition are set off with commas; those that restrict preceding material are not.
|1.||Nonrestrictive apposition merely adds information to something already identified:
John's play, Phalanges, was a flop. (John wrote only one play.)
|2.||Restrictive apposition completes the identification:
Shakespeare's play Macbeth is on the reading list (one of many plays by Shakespeare).
|3.||Relationships take commas or not depending upon how many
relatives of the same kind there are. If there is but one, use commas:
my wife, Nellie, and my son, Bob, came too (only one wife and only one
Bob and his wife, Ann; but Bob and wife Ann.
If there are
two or more, no commas:
her sister Millie and her cousin Karen came too
(more than one sister and more than one cousin)