Forbidden knowledge, which is different from secret knowledge, is used to describe forbidden books or other information to which access is restricted or deprecated for political or religious reasons. Forbidden knowledge is commonly not secret, rather a society or various institutions will use repressive mechanisms to either completely prevent the publication of information they find objectionable or dangerous (censorship), or failing that, to try to reduce the public's trust in such information (propaganda). Public repression can create paradoxical situation where the proscribed information is generally common knowledge but publicly citing it is disallowed.