Pronouns and adjectives are two different parts of speech, but a pronominal adjective takes the form of a pronoun while serving the function of an adjective. The usage of pronominal adjectives is governed by set grammar rules that help distinguish these adjectives from the pronouns that they mimic. Furthermore, these adjectives can be divided into several common subcategories, including but not limited to demonstrative, relative and distributive adjectives.
All adjectives modify nouns. Words that describe the appearance, characteristics, number or other identifying features of a person, place, thing or idea usually are adjectives. In most instances within the English language, adjectives appear directly before the noun they describe. An adjective rarely appears on its own without any noun present.
Pronouns replace nouns. Typically, in everyday English speech or writing, the original noun being discussed is mentioned earlier in the discussion, providing the necessary context for the pronoun that is used later. Replacing that specific noun with a pronoun helps reduce repetitiveness, creating a smoother-flowing passage of speech or writing.
A pronominal adjective cuts down on redundancy in a similar manner as a pronoun does, but instead of replacing a repetitive noun, it usually replaces a determining term or phrase. For example, instead of saying "the orange cat," one might say "that cat." The "that" in "that cat" is a pronominal adjective. Pronominal adjectives modify nouns by determining the specific noun in question, so they are also occasionally referred to as determining adjectives.
In most cases, the pronominal adjective in use accompanies the noun that it modifies. In the sentence "This is his book," the word "this" is a pronoun because it acts as the subject of the sentence and replaces whatever noun phrase would refer to the specific book in question. On the other hand, in the sentence "This book is his," the word "this" is a pronominal adjective because it modifies and determines the subject noun "book."
These adjectives and the nouns that they modify must also agree in number. A singular noun requires a singular pronominal adjective, and a plural noun requires a plural adjective. For example, writing "this pen" and "these pencils" are both correct. Writing "these pen" or "this pencils" is incorrect.
Several subcategories exist to further classify pronominal adjectives. Demonstrative pronominal adjectives — "this," "that," "these" and "those" — point to a definitive object. Relative pronominal adjectives — "which" and "what" — identify an object in relation to other objects. Distributive pronominal adjectives — "each," "every," "either" and "neither" — modify nouns that are distributed separately and singularly. Many linguists use additional subcategories as well.