Argumentum ad hominem means argument toward human; and used when the criticism/objection is directed against a certain individual/society in person, rather than against the opponent’s thoughts/ideas.

Augustine had offered to prove that by Cicero’s definition, the Romans never had a republic: “I shall attempt to show that no such commonwealth ever existed, because true justice was never present in it” (City of God II.21, p. 80), since the Romans did not obey the true God (ibid, XIX.21). But this is an argumentum ad hominem.