Sacred Congregation of the Index

The Index Librorum Prohibitorum (English: List of Prohibited Books) was a list of publications deemed heretical, or contrary to morality by the Sacred Congregation of the Index (a former Dicastery of the Roman Curia) and thus Catholics were forbidden to read them.

The 9th century witnessed the creation of what is considered to be the first index, called the Decretum Glasianum, but it was never officially authorized. Much later, a first version (the Pauline Index) was promulgated by Pope Paul IV in 1559, which Paul F. Grendler believed marked "the turning-point for the freedom of enquiry in the Catholic world", and which lasted less than a year, being then replaced by what was called the Tridentine Index (because it was authorized at the Council of Trent), which relaxed aspects of the Pauline Index that had been criticized and had prevented its acceptance.

The 20th and final edition appeared in 1948, and the Index was formally abolished on 14 June 1966 by Pope Paul VI.

The aim of the list was to protect the faith and morals of the faithful by preventing the reading of theologically, culturally, and politically disruptive books. Books thought to contain such errors included works by astronomers such as Johannes Kepler's Epitome astronomiae Copernicanae, which was on the Index from 1621 to 1835, and by philosophers, like Immanuel Kant's Critique of Pure Reason. The various editions of the Index also contained the rules of the Church relating to the reading, selling and pre-emptive censorship of books—editions and translations of the Bible that had not been approved by the Church could be banned.

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