How did John Duns Scotus explain the individuality of a person such as Socrates?

John Duns Scotus explained the individuality of a person like Socrates through his doctrine of "thisness," or haecceitas.12

While Duns Scotus acknowledged that common natures—such as humanity—are real and exist within many individuals, he argued that these common natures alone do not account for what makes a specific person unique. Instead, he proposed that the individuality of a specific being is derived from an added positive reality that distinguishes that individual from others who share the same common nature.12

By identifying this "individual difference" as haecceitas, Duns Scotus provided an original development to the medieval realism of universals, asserting that this principle is what ultimately makes a common nature a specific, singular individual.12