Syllabus of Errors

The Syllabus of Errors (Latin: Syllabus Errorum) was a document issued by the Holy See under Pope Pius IX on December 8, 1864, the Feast of the Immaculate Conception, on the same day as the Pope's encyclical Quanta cura. It condemned a total of 80 errors or heresies, and through that promulgated Church teaching on a number of philosophical and political questions, and referred to the Church's teaching on these matters as given in a number of documents issued previously. The document itself was an attack on liberalism, modernism, moral relativism, secularization, and the political emancipation of Europe from the tradition of Catholic Monarchies.

Reaction amongst Catholics was mixed, while that coming from Protestants was uniformly negative. It remains a controversial document, and has been cited on numerous occasions by both Catholic traditionalists seeking to uphold traditional Catholic values and anti-Catholics seeking to criticize the Church's positions.

The Syllabus was made up of phrases and paraphrases from earlier papal documents, along with index references to them, and presented as a list of "condemned propositions". For instance, in condemning proposition 14, "Philosophy is to be treated without taking any account of supernatural revelation", the Syllabus asserts the truth of the contrary proposition—that philosophy should take account of supernatural revelation. The Syllabus does not explain why each particular proposition is wrong, but it cites earlier documents to which the reader can refer for the Pope's reasons for saying each proposition is false. With the exception of some propositions drawn from Pius' encyclical Qui pluribus of November 9, 1846, all the propositions were based on documents that postdated the shocks to the Pope and the papacy of the Revolutions of 1848 (see Italian unification).

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