Essentially a follow-up to the better-known Mirari vos of 1832, Singulari Nos focused strongly on the views of French priest 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.

In October 1830, Lamennais, Jean-Baptiste Henri Lacordaire, and Charles Forbes René de Montalembert founded the newspaper, L'Avenir, which advocated an enlarged suffrage, separation of church and State, universal freedom of conscience, instruction, assembly, and the press, views were opposed by the French bishops.

These events placed the Sovereign Pontiff between two opposite dangers; his fears from France are intelligible enough; Austria, on the other hand, had always been supposed to covet the portion of the pontifical states on the north of the Apennines; and the suspicion had been so strong in Rome, in 1821, that the government had not allowed the Austrian forces to pass through the city on their way to Naples.

She alleged that she could not possibly have any interested views as regards the Italian peninsula, either revolutionary or ambitious, and she offered to place a force at the Pope's disposal to defend him against all emergencies.

In 1834 he responded with a short, biting book, Paroles d'un croyant ("Words of a Believer"), in which he denounced all authority, civil as well as ecclesiastical.

By Our apostolic power, We condemn the book: [...] It corrupts the people by a wicked abuse of the word of God, to dissolve the bonds of all public order and to weaken all authority.

[11] Lamennais's brother Jean-Marie, by that time Superior General of the Mission Priests of the Immaculate Conception, repudiated Paroles and the two never met again.

He notes that Dom Prosper Guéranger, who was an early Lamennais follower, became the principal agent of a liturgical revival and a uniform Roman Liturgy.