Quadragesimo Anno §111

¹¹¹ Socialism, against which Our Predecessor, Leo XIII, had especially to inveigh, has since his time changed no less profoundly than the form of economic life. For Socialism, which could then be termed almost a single system and which maintained definite teachings reduced into one body of doctrine, has since then split chiefly into two sections, often opposing each other and even bitterly hostile, without either one however abandoning a position fundamentally contrary to Christian truth that was characteristic of Socialism.