Index Librorum Prohibitorum

Index Librorum Prohibitorum

Knowledge is power, but it can also be dangerous, or at least that was the rationale behind the centuries long ban on texts considered to be heretical, immoral, or otherwise contrary to the teachings of the Catholic Church. They weren’t entirely wrong: some of the most popular early printed works addressed topics such as witches and vampires, resulting in hysteria and witch trials. There was also widespread violence in the course of the Reformation and various religious conflicts culminating in the Thirty Years’ War.
Works directly challenging official positions of the Catholic Church be they the writings of Protestant theologians like Luther and Calvin, the heliocentrism of Copernicus, Kepler, and Galileo, or Kant’s philosophical writings were officially banned. Many Protestant scholars were generally blacklisted, even those writing about subjects that had nothing to do with religious dogma, although some received dispensations. Any secular or religious text deemed problematic between the mid-17th and the mid-20th centuries was listed in the Index Librorum Prohibitorum and faithful Catholics were banned from reading them save for those scholars deemed wise enough to study them “safely”. The original 1559 edition, referred to as the Pauline Index, is presented here.

Origins of the List of Prohibited Books

The Church attempted to ban various books deemed heretical during the Middle Ages, the 9th century Decretum Gelasianum being the most notable, but the scarcity and expense of books limited these considerations to the clergy. However, the invention of the printing press put books into the hands of laymen and action had to be taken to “protect” them from “dangerous” knowledge. Originally introduced in 1557, the Index was quickly withdrawn for unknown reasons before a new index was published in 1559 that banned the collective works of ca. 550 authors in addition to hundreds of individually prohibited titles. However, many people including members of Catholic intellectual circles felt that the censors were too zealous in performing their task and after the Council of Trent, the more moderate Tridentine Index was promulgated in 1564 and served as the basis of all later lists until the 1897 Index Leonianus Pope Leo XIII (1810–1903).

Who Decided What Books Were Banned?

A special department called the Sacred Congregation of the Index was created in 1571 with the purpose of researching banned texts, updating the list regularly, and identifying works that could be taken off the list if certain corrections were made to them; these works were referred to as donec corrigatur or “forbidden until corrected”. This group met several times per year to review and discuss various works and documented these discussions. Between these meetings, individual works were examined by a pair of clerics who would present their findings and the group would collectively decide whether or not to add works to the list. The final verdict belonged to the pope, who would decide by consulting the records of these discussions. Works previously added to the Index could later be removed from it, e.g. the 1758 edition removed the prohibition on works arguing for a heliocentric model of the universe.

The Later Editions

After the list was updated in 1897, the subsequent editions became more nuanced and sophisticated: rather than banning or not banning authors, they rated them on their supposed level of harmfulness and specified individual passages for correction rather than denouncing entire books. Individual books continued to be added to the Index until the last edition was published in 1948 when the titles numbered 4,000 in total, most of which were censored due to being heretical, morally deficient, or overtly sexual in nature. The Sacred Congregation of the Index was merged with the Holy Office in 1917 and is now called the Dicastery for the Doctrine of the Faith. When the Index was finally abolished in 1966, it was not because the Church felt that it no longer possessed its moral force as a guide for protecting Christians from endangering their faith or morality, but because the Church recognized that it simply no longer possessed the power of canon law to enforce its prohibition.