Index of Forbidden Books

The Index Librorum Prohibitorum (English: List of Prohibited Books) was a list of publications deemed heretical, anti-clerical or lascivious, and therefore banned by the Catholic Church.

The 9th century witnessed the creation of what is considered to be the first index, called the Decretem 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 heretical and immoral 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.

Catholic canon law still recommends that works concerning sacred Scripture, theology, canon law, church history, and any writings which specially concern religion or morals, be submitted to the judgment of the local ordinary. The local ordinary consults someone whom he considers competent to give a judgment and, if that person gives the nihil obstat ("nothing forbids") the local ordinary grants the imprimatur ("let it be printed"). Members of religious institutes require the imprimi potest (it can be printed) of their major superior to publish books on matters of religion or morals.

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