What pronouns and their antecedents should do

AGREE

Think of how subjects and verbs must match in number and person.

In grammar, pronouns must match their antecedents (the words they replace) in number, gender, and person—this is called "agreement." The clue plays on that rule by framing it as something pronouns and antecedents should do, hinting at the word "agree." It’s a straightforward definition with a slight twist, turning a grammatical concept into a verb. The answer is simply "AGREE," fitting both the meaning and the wordplay.