’Fides et Ratio’ (Papal Encyclical on Faith and Reason)

It was the first encyclical since Pope Leo XIII's 1879 Aeterni Patris to address the relationship between faith and reason.

The encyclical posits that faith and reason are not only compatible, but essential together. He starts with "Faith and reason are like two wings on which the human spirit rises to the contemplation of truth;" Faith without reason, he argues, leads to superstition. Reason without faith, he argues, leads to nihilism and relativism.