Premodifiers are words that are part of a noun phrase, that come before the noun that they modify. These words provide more specific information, which is the process of modification, that helps indicate one particular instance of a noun, rather than leaving it open. For example, the word "cat" is a noun and when used alone it can refer to any type of animal that is part of the feline family. Premodifiers can be provided, however, to refer to a particular one, "the cat," or to give additional information about it such as "the large, brown cat."
There are both premodifiers and postmodifiers that can be used as part of a phrase to help modify a noun. It is important to identify them as part of the noun phrase, since any pronoun used to refer to them indicates the entire phrase and not just the noun itself. For example, in the sentence "My car is blue," the word "my" is a premodifier that specifies exactly what is being referred to by the noun "car." When a pronoun is used afterward, such as "My car is blue and it is very fast," the word "it" refers to not only "car" but to "my car" and so it replaces all premodifiers as well as the noun.
Premodifiers commonly consist of one or more words that include articles, adjectives, and possessive pronouns. Both indefinite articles, such as "a" or "an," and definite ones like "the" can be used in this way, and refer to either a general item or a specific noun. Adjectives that describe an object, such as "orange" or "large" are among the most common premodifiers and verbs with the suffix "-ing" can be used in this same way. Possessive pronouns help modify nouns by indicating ownership over an object such as "my book" or "their house."
Unlike premodifiers, postmodifiers come after the noun that they describe, but they are also part of the same noun phrase. For example, the sentence, "The tomcat with large eyes creeps through the grass," includes a single noun phrase with both pre and postmodifiers. The noun is simply "tomcat" with a premodifier of the definite article "the;" the postmodifiers are in the form of a prepositional phrase "with large eyes" that provide additional information to specify which cat is being referred to. All of this is part of the same noun phrase, since it could be replaced with a single pronoun and become "He creeps through the grass."