In English grammar, predicate nominative is the traditional term for a noun, pronoun, or another nominal that follows a linking verb, which is usually a form of the verb "be." The contemporary term for a predicate nominative is a subject complement.
In formal English, pronouns that serve as predicate nominatives are usually in the subjective case such as I, we, he, she and they, while in informal speech and writing, such pronouns are often in the objective case such as me, us, him, her and them.
In her 2015 book "Grammar Keepers," Gretchen Bernabei suggest that "if you think of the linking verb as an equal sign, what follows it is the predicate nominative." Further, Bernabei posits that "if you switch the predicate nominative and the subject, they should still make sense."
Direct Objects of Linking Verbs
Predicate nominatives are used with forms of the verb be, and as a result, answer the question of what or who is doing something. Therefore, predicate nominatives can be considered to be identical to direct objects except that predicate nominatives are a more specific example of words that are the subjects of linking verbs.
Buck Ryan and Michael J. O'Donnell use the example of answering a telephone to illustrate this point in "The Editor's Toolbox: A Reference Guide for Beginners and Professionals." They note that although it is commonly accepted to answer a phone with "It's me," "It is I" is the correct usage, as is "This is he" or "This is she." Ryan and O'Donnell state that "You know the subject is in the nominative case; he or she is the predicate nominative."
Predicate Adjectives and Kinds of Nominatives
Although all predicate nominatives receive the same treatment in cognitive grammar, there are two distinct kinds of referential identification, which depend on how the sentence quantifies the subject. In the first, the predicate nominative indicates the referential identity of the subject and predicate nominals such as "Cory is my friend." The other categories the subject as a member in a category such as "Cory is a singer."
Predicate nominatives should also not be confused with predicate adjectives, which further define adjectives in a sentence. However, both can be used in a sentence as part of a single subject complement, as Michael Strumpf and Auriel Douglas put it in their 2004 book "The Grammar Bible."
Strumpf and Douglas use the example sentence of "He is a house husband and quite content" to emphasize that the predicate nominative husband to the subject (he) via a linking verb (is) acts in tandem with the adjective content to describe the man. They note "both types of subject complements follow a single linking verb," and most modern grammarians view the whole phrase as a single subject complement.