The tendency of highly organized religious and ideological groups is to become more and more proscriptive regarding the behaviour of their members and their private thoughts and reading habits. Lists of disapproved books and ideas may be circulated. Schools operated by religious denominations or by statist regimes may not provide some critically acclaimed modern and classic works to their students, and teachers may not even mention disapproved authors or concepts.
A document entitled, 'Syllabus of Errors' was put forth by the Vatican in 1864. Among its 10 sections and 80 theses it listed 'errors' of thought and behaviour as applied to Bible societies, secret societies, socialism, rationalism, religious latitudinarianism, and wrong conceptions concerning the temporal power of the Pope. Put positively, the Syllabus argued for state religion, temporal power for the Church, the subordination of civil law to ecclesiastical law in religious matters, along with many other relics of mediaeval Church thinking. The Catholic Encyclopaedia notes that even today 'the Syllabus must be accepted by all Catholics since it comes from the Pope'. In Communist Russia and China, 'errors' contradicting orthodox Marxism-Leninism were identified and condemned and bore such names as Trotskyism, revisionism, deviationism, etc.