 In part I of his Dialogus, books  3  and  4  (c. 1334) Ockham discusses heresy and heretics, arguing that for someone to be a heretic it is not enough that something that person believes is heresy, he or she must also believe it “pertinaciously”, and to discover pertinacity it is often necessary to enter into discussion to find whether the person is ready to abandon the error when it is shown to be such. For example, a layperson who believes undogmatically a doctrine that is in fact heresy, until it has been shown to be heresy in a way adapted to that person’s understanding, may maintain it “a thousand times”, even in the face of contradiction by bishop or pope, without being a heretic  (1 Dialogus 4.23).  On the other hand, a pope who tries to impose a false doctrine on others is known to be pertinacious precisely from the fact that he is trying to impose false doctrine on others, and a pope who becomes a heretic automatically ceases to be pope. Thus ordinary Christians (or a pope arguing as a theologian and not purporting to exercise papal authority) can argue for a heresy as long as they are open to evidence and make no attempt to impose their belief on others, whereas a pope who tries to impose a heresy immediately ceases to be pope and loses all authority. Christians must defend dissidents who are upholding a position that may possibly be the truth against a possibly heretical pope, until the uncertainty is resolved by discussion. This is an argument for freedom of discussion within the Church, though not for toleration in general (McGrade 1974: 47–77; McGrade, Kilcullen, and Kempshall 2001: 484–95; Kilcullen 2010a).