In demonstrating that the bull Quia vir reprobus was full of heretical errors, Ockham identified himself as a theologian who was determined to combat papal heresy. The problem of papal heresy, which had perplexed canonists and theologians alike, inevitably raised for Ockham a number of ecclesiological questions. Is it possible for a pope – the vicar of Christ and successor of St Peter – to fall into heresy? If it is, who can judge a pope and how? What sanction should be applied to a heretical pope? Ockham did not fail to discern these – to mention only three – crucial, if not novel, issues. During the course of writing the Opus nonaginta dierum, he was probably aware of the need to embark on an investigation of these questions. By late 1334, Part I of the Dialogus, which was still more voluminous than the Opus nonaginta dierum, had been written for this purpose.

I Dialogus, as the title suggests, takes the form of a dialogue between a master and a disciple.