The claim that under certain conditions the doctrinal and moral teaching of a Church cannot err applies particularly to the Roman Catholic Church and to the Pope. Infallibility is derived from the belief that God has intervened in human history and has given man the possibility of assurance in religious matters; also from the belief that the Church is not a human creation, its essential structure and nature having been determined by Christ. The Church is seen as the extension of Christ in time, and the Pope as the Supreme teacher in the Church, guided by Christ. Papal declarations may be strongly adhered to, particularly by members of traditional or underdeveloped societies and this may retard social progress (for example, with birth control and abortion). The Roman Catholic claims to the primacy of the bishopric of Rome among bishops, and the infallibility of ex cathedra teachings, are the major impediments to ecumenicism and Church reunification.
The papal and magisterial errors errors fall into four main areas:
1. Theological errors taught by popes or central Roman authorities, including: declaration that it is necessary for salvation for every human person to be subject to the bishop of Rome (Boniface VIII, 1302); declaration that the 1590 version of the Vulgate (riddled with errors) was forever valid and unalterable (Sixtus V, 1590), although it had to be replaced within two years; variety of statements made by the Pontifical Bible Commission (1906-1933) subsequently rejected by all or most Catholic Biblical scholars.
2. Moral teachings which have been later reversed or ignored, including those on: slavery, usury, contraception and family planning, and prohibition of sex during menstruation.
3. Errors of moral action or insight by Rome, whether popes or officials, including: calling for the Crusades (Urban II); allowing the use of torture by the Inquisition (Gregory IX); calling for the ghettoization of Polish Jews (Benedict XIV); papal attacks on the availability of the Bible to the laity.
4. Errors of moral action by Councils, including: anathematizing women who cut off hair (Gangra, 325-381); imposition of symbol on the Jews (Lateran VI, 1215).
The historical church can never claim to be infallible or inerrant in regard to any of its decisions or traditions, for all of them are relative to historical conditions. Even the relative authority which can be claimed for a decision or tradition will depend upon its adherence to the mandate: "As the Father has sent me, even so I send you".
The errors of the ecclesiastical teaching office in every century have been numerous and indisputable: a close scrutiny of the Index of Forbidden Books would be particularly revealing in this respect. An yet the teaching office constantly found it difficult to admit these errors frankly and honestly. Mostly the correction was only made "implicitly," in a veiled way, without any frankness and particularly without admitting the mistake. It was feared that awareness of the admitted falliblity of certain important decisions would restrict or even finally shut out the prospect of claiming infallibility for certain other important decisions. (Hans Kueng).
Although much of the activity and statements of Catholic officials in the past can be convincingly explained by reference to the presumptions and biases of the time, the difficulty with this approach is for writers, including modern popes, who wish to argue that moral values are absolute and timeless, despite earlier statements condoning the inquisition and some forms of slavery. The gradualist and non-absolutist approach of some modern Catholic Apologetics for the Church's approach to slavery (and especially the slave trade) in the past conveniently ignores this absolutism, typically retreating to notions that the Church was doing the best it could. Unfree servitude, where a person has sold his or herself is still considered, if inadvisable, as consistent with natural law.
Some of the "errors" cited, do not logically at least, invalidate claims to magisterial or papal infallibility. The main defense would be that the error was not "asserted as infallible", or that the person making the error was acting in an unofficial capacity.
In the writings of non-Catholic authors against the definition of Papal Infallibility, the dogmatic propositions on the unity of the Church, the necessity of belonging to it for the attainment of eternal salvation, the position of the Pope as supreme head of the Church, and the duty thence arising of submission to the Pope in order to belong to the Church and thus to attain salvation (Boniface VIII, 1302) have been used against the papal primacy in a manner not justified by its content. The statements concerning the relations between the spiritual and the secular power are of a purely historical character, so far as they do not refer to the nature of the spiritual power, and are based on the actual conditions of medieval Europe.
In fact the Bull seems to fulfill all the requirements of an infallible papal statement as laid down in 1871 at the First Vatican Council. The final line " we declare, we proclaim, we define that it is absolutely necessary for salvation that every human creature be subject to the Roman Pontiff" is in the form used for the declarations on the Immaculate Conception and the Assumption, for instance. As it stands, this doctrine has been repudiated by the modern Catholic Church. Even in the 19th century, Pius IX was clear that innocent people of goodwill could be saved. The Second Vatican Council specifically asserts that people in all religions can be saved. Although some later commentators have tried to salvage the position - usually by asserting that only the Church has the right to interpret its own documents, there is little doubt that there has been a def fact reversal in Church teachings around this "definitive" papal teaching.