Appositives.
Today we discuss appositives. An appositive is a noun, noun phrase, or series of nouns that identifies the same person, place, or thing by a different name. Whether to use commas with an appositive depends on whether it is restrictive or nonrestrictive, which is a question of meaning. Compare the following examples:
My friend Angela went hiking in Ridgefield National Wildlife Refuge with me last weekend.
Stephen’s car, a ‘65 red convertible Mustang, was the envy of his friends.
In the first example, the absence of commas indicates that “Angela” is restrictive (or necessary), because the author has more than one friend (really); so “Angela” identifies which friend is being referred to. In the second example, the author had only one car; so the commas indicate that “a ‘65 red convertible Mustang” adds only additional, parenthetical information.
Finally, although an appositive usually follows the word it explains or identifies, it may also precede it, e.g.:
The first state to ratify the U. S. Constitution, Delaware is home to Dogfish Head Craft Brewery.
That is all for now ...