Sedevacantists defend their position using numerous arguments, including that particular provisions of canon law prevent a heretic from being elected or remaining as pope. Paul IV's 1559 bull, "Cum ex apostolatus officio", stipulated that a heretic cannot be elected pope, while Canon 188.4 of the 1917 Code of Canon Law provides that a cleric who publicly defects from the Catholic faith automatically loses any office he had held in the Church. A number of writers have engaged sedevacantists in debate on some of these points. Theologian Brian Harrison has argued that Pius XII's conclave legislation permitted excommunicated cardinals to attend, from which he argues that they could also be legitimately elected. Opponents of Harrison have argued that a phrase in Pius XII's legislation, "Cardinals who have been deposed or who have resigned, however, are barred and may not be reinstated even for the purpose of voting", though it speaks of someone deposed or resigned from the cardinalate, not of someone who may have incurred automatic excommunication but has not been officially declared excommunicated, means that, even if someone is permitted to attend, that does not automatically translate into electability. While Sedevacantists' arguments often hinge on their interpretation of modernism as being a heresy, this is also debated.