Those who write treatises on Duties (De Officiis) as, for instance, Cicero, St. Ambrose, Grotius, Opalenius, Sharrok, Rachelius, Pufendorf, as well as the Casuists, teach that there are cases where one is not obliged to return to its owner a thing deposited: for example, one will not give back a dagger when one knows that he who has deposited it is about to stab someone.