An antecedent is the noun, noun phrase, or a noun clause that a pronoun refers to in a sentence. It is normally found in a sentence before a pronoun—the “ante” in the word means “before”—so it may not be exactly appropriate to ask when and where it’s used. The antecedent is presumed to be already present somewhere in the sentence, and what’s needed in grammar is that any pronoun in the sentence that refers to this antecedent must agree with it in person (whether first, second, or third person), case (whether nominative or subjective, objective, or possessive) and number (whether singular or plural).
For example, the noun “Roberto” is the antecedent of the pronoun “he” in this basic sentence: “Roberto finally found the book he had been looking for.”
An antecedent need not be a noun; it can also be a noun phrase, as in this sentence: “The basic computer course that Ana wants to take is currently offered by the school, but it costs twice her budget for it.” Here, the antecedent is the entire noun phrase ““the basic computer course that Ana wants to take,” and “it”—used twice in the sentence—is a pronoun that refers to that antecedent.
And an antecedent can also be a noun clause, as in this sentence: “What transpired during his long meeting with his boss disturbed Armando, and it gave him bad dreams for several nights.” Here, the noun clause “what transpired during his long meeting with his boss” is the antecedent of the pronoun “it” in that sentence. In the noun clause, the noun “Armando” is the antecedent of the possessive pronoun “his,” which is used twice—first to modify “long meeting,” then to modify “boss.”
When the antecedent is in plural form or is a compound noun—meaning that it consists of two or more nouns—the pronoun that refers to that antecedent must also be in plural form, as in this sentence: “His manager and his wife are demanding quality time from Steve, and they both won’t accept compromises.” Here, “his manager and his wife” is a compound antecedent, so the pronoun referring to it is the plural-form “they.” Note that the noun “Steve” is the antecedent of the possessive pronoun “his”—used twice—in the noun phrase.
I hope that this discussion has clarified in your mind the grammar concept of “antecedent” and its relation to pronouns.
