Singulari Nos
Singulari Nos (subtitled On The Errors Of Lammenais) was an encyclical issued on June 25, 1834 by Pope Gregory XVI
Essentially a follow-up to the better-known Mirari Vos of 1832, Singulari Nos focused strongly on the doctrinal errors of French priest Hughes Felicité Robert de Lamennais, who did not see any contradiction between Catholicism and then-modern ideals of liberalism and the separation of Church and State.
Although Mirari Vos had condemned Lammenais, it was Singulari Nos that effectively removed his ideas from the thought of those employed by the Catholic Church until the pontificate of Pope Leo XIII. Some liberal historians of the papacy argue that these two encyclicals are of great importance as the point at which the official teaching of the Catholic Church broke for good with efforts to embrace the modern world.