In Durant's opinion the central obstacle to the reform of the church was the conflict between law and government. In itself, of course, this opinion was by no means new. Ever since the papacy had risen to lead the medieval church there had been doubts about the legitimacy of its policies. One need not turn to the party of the emperor and his Ghibelline supporters or to Cathar heretics to demonstrate the depth of such doubts; St Bernard could not have put it more soberly when he announced that the papal plenitude of power was not the same as a plenitude of justice. Hence thinkers of unquestionably orthodox intentions, with deep roots in the ancient traditions of the church, had attempted to limit papal government long before the days of William Durant. Canonists, not heretics, were responsible for showing that, above and beyond the articles of faith, there was a ‘state of the church’ which the pope was not at liberty to change; canonists, not heretics, taught that a pope who fell into heresy or committed outrageous crimes could be deposed from office; canonists, not heretics, declared that councils were greater than popes.