A noun is a part of speech that refers to a person, a thing or an idea or concept. That's one way to identify a noun, but a better way to distinguish a noun from other parts of speech is to look at its position and function in a sentence. A noun can be a subject, an object of a verb or an object of a preposition. It can also be an appositive.
An appositive noun is a noun that adds additional information about another noun in a sentence. For example, in the sentence "My brother John is very funny," the word "John" is an appositive noun.
What Is a Noun?
There are some specific morphological features that can help you distinguish nouns from other parts of speech. For example, nouns often follow a determiner (the, a or an). Nouns can be common or proper. Proper nouns are names and begin with a capital letter. Nouns in English can be singular or plural (apple vs. apples). They can be possessive and appear with the possessive suffix 's (Jenny’s apple).
Another good way to tell that a word is a noun is to look at its role in a sentence. Some of the common roles for a noun are a subject, direct object, indirect object and an object of a preposition. Some examples include:
Mark likes ham. “Mark” is the subject and “ham" is the direct object.
Mark gave Kylie some ham. "Mark" is the subject and “Kylie” is the indirect object.
Mark enjoys going to restaurants with friends. "Mark" is the subject and “friends” is the object of a preposition.
What Is an Appositive Noun?
An appositive noun is a noun whose role is to clarify or explain something about another noun in a sentence. It immediately follows the noun that it modifies. For example, in the sentence My teacher is very kind, “my teacher” is the subject of the sentence. You can add additional information about the teacher in the same sentence and say My teacher Ms. Pickles is very kind. In this case, "Ms. Pickles" is the appositive noun. It supplies additional information about the subject. It can be omitted and the sentence will still be grammatically correct. Some more appositive examples include:
My brother John is very funny.
In the airport we met James, my uncle.
An appositive can be a single word or a phrase, in which case it is called an appositive phrase. It can modify a subject or an object of a sentence. For example, in the following sentence, the phrase “my favorite teacher at school” is an appositive phrase modifying the subject “Ms. Pickles.”
Ms. Pickles, my favorite teacher at school, gives us math homework every week.
In the next sentence, the phrase “the highest mountain in North America” is an appositive phrase that is modifying the object of the sentence, “Mount McKinley.”
Next year we’re going to climb Mount McKinley, the highest mountain in North America.
Do Appositives Need a Comma?
Whether or not an appositive phrase is separated by commas depends on whether it is a restrictive or a nonrestrictive appositive. If the presence of the appositive is needed to understand the identity of the noun it modifies, then it is called a restrictive appositive, and it is not set off with commas. If the appositive is completely optional, and its presence in the sentence is not necessary to help understand the identity of the noun, then it is called a nonrestrictive appositive, and it is set off with commas.
For example, in the sentence My teacher Ms. Pickles sings in a choir on Saturdays, the phrase "Ms. Pickles" is a restrictive appositive. Without it we still understand the meaning of the sentence but wouldn’t know which teacher is being talked about.
On the other hand, if you say My science teacher, Ms. Walters, is very strict, the presence of the appositive phrase "Ms. Walters" is completely optional since you presumably only have one science teacher.