Pius XI Quotes
If Socialism, like all errors, contains some truth (which, moreover, the Supreme Pontiffs have never denied), it is based nevertheless on a theory of human society peculiar to itself and irreconcilable with true Christianity. Religious socialism, Christian socialism, are contradictory terms; no one can be at the same time a good Catholic and a true socialist.
Pius XI. Quadragesimo Anno. Libreria Editrice Vaticana, 15 May 1931.
Pope Pius XI (Italian: Pio XI), born Ambrogio Damiano Achille Ratti, was head of the Catholic Church from 6 February 1922 to his death in 1939. He was the first sovereign of Vatican City from its creation as an independent state on 11 February 1929. He took as his papal motto "Pax Christi in Regno Christi," translated "The Peace of Christ in the Kingdom of Christ."