Where two nouns or two noun phrases are placed side by side they are said to be in apposition. In writing fiction and in academic articles, the identification and renaming assumes great importance.
They are often introduced by such words as namely, or for example, or that is, or and these were or less common, to wit. They help clarification.
The main issue for the writer is whether the second noun or noun phrase needs to be set off with commas. In other words, is the second noun or noun phrase essential to the meaning of the sentence? If it is, then commas serve no useful purpose because they would otherwise suggest that what is enclosed in parentheses is not strictly necessary, when, in fact, it is. If, on the other hand, the noun or noun phrase is not essential to the meaning of the sentence they can be set off with commas.
Examples: non-restrictive appositive noun
My sister-in-law, Pauline, is experiencing problems with her car not starting properly.
Usain Bolt, Olympic champion and a member of the Jamaican team, has fans across the world.
In both the above cases, the noun (first example) and the noun phrase (second example) illustrate how to use the appositive correctly. Each appositive is non-essential to the sentence. In the first case, the person in question is my sister-in-law and she is the only sister-in-law I have. Readers who are unfamiliar with my family would assume, quite correctly in this case, that I have included Pauline’s name in the sentence to provide additional information, not essential information. In the second example, the person reading this sentence would have had to live under a rock all the time that Usain Bolt has been in action for them not to be aware of how well known Bolt is. So, placing his fame in parentheses is correct.
Examples: restrictive appositive noun
There are, however, occasions when the noun or noun phrase cannot be separated with commas because the information is essential for it to make sense to the reader. Here are some examples:
My best friend, Peter Thomas, has his sixty-sixth birthday next April.
The story The Winner is written by David Baldacci. It is about a woman who cheats the United States Lottery.
The author Kerry Barnes has written a trilogy about the Vincent family.
There is another test that the writer can use to check on whether they have punctuated the appositive noun or noun phrase in the sentence correctly. When the sentence is read either silently or out loud, the reader can often judge where a comma is required, just by the pronounced emphasis on where the comma needs to be placed.
A Alex, my brother, sang in the choir this morning.
B Athlete Iona Lake won the 3000-metre race last week.
C My friend John has bought over one hundred and twenty cars in his lifetime.
D Ernest Hemingway, the American novelist, is often referred to as a minimalist writer. He wrote Less is More: Literary Minimalism in American Short Story.
Answers are as follows:
A Alex, my brother, sang in the choir this morning. [non-restrictive] B Athlete Iona Lake won the 3,000-metre race last week. [restrictive] C My friend John has bought over one hundred and twenty cars in his lifetime. [restrictive] D Ernest Hemingway, the American novelist, is often referred to as a minimalist writer wrote ‘Less is More: Literary Minimalism in American Short Story. [non-restrictive]
Rationale for this on request.