cui bono

a Latin phrase from Cicero. It means "to whom for a benefit," or "who profits by it?" not "to what good purpose? for what use or end?" as is sometimes said. From cui "to? for whom?," an old form preserved here in the dative form of the interrogative pronoun quis "who?" (from PIE root *kwo-, stem of relative and interrogative pronouns) + bono "good" (see bene-).