Rules for writers, Tenth edition - Diana Hacker, Nancy Sommers 2021

Use the subjective case (I, you, he, she, it, we, they) for subjects and subject complements
Distinguish between pronouns such as I and me
Grammar

The personal pronouns in the following chart change what is known as case form according to their grammatical function in a sentence. Pronouns functioning as subjects or subject complements appear in the subjective case; those functioning as objects appear in the objective case; and those showing ownership appear in the possessive case.

Pronouns in the subjective and objective cases are frequently confused. Most of the rules in this section specify when to use one or the other of these cases. Section 24f explains a special use of pronouns and nouns in the possessive case.

24a Use the subjective case (I, you, he, she, it, we, they) for subjects and subject complements.

When personal pronouns are used as subjects, ordinarily your ear will tell you the correct pronoun. Problems sometimes arise, however, with compound word groups containing a pronoun.

When a pronoun is used as a subject complement (a word following a linking verb), your ear may mislead you, since the incorrect form is frequently heard in casual speech. (See “Linking verbs and subject complements,” 48b.)