In the motu proprio Fin dalla prima, of December 18, 1903, Saint Pius X summarizes the doctrine of Leo XIII on social inequalities:
1. Human society, as God established it, is composed of unequal elements, just as the members of the human body are unequal. To make them all equal would be impossible, and would result in the destruction of society itself (encyclical Quod Apostolici muneris).
2. The equality of the various members of society is only in that all men originate from God the Creator; that they were redeemed by Jesus Christ, and that they must be judged by God and rewarded or punished in strict accordance with their merits and demerits (encyclical Quod Apostolici muneris).
3. Wherefore, it results that, in human society, it is God’s will that there should be princes and vassals, proprietors and proletarians, rich and poor, learned and ignorant, nobles and plebeians, all of whom, united in the bond of love, should help one another to achieve their final end in Heaven, and their material and moral well-being here on earth (encyclical Quod Apostolici muneris).
(Acta Sanctae Sedis [Rome: Ex Typographia Polyglotta, 1903-1904], Vol. 36, p. 341.)
In Nobility and Analogous Traditional Elites, best-selling author Professor Plinio Corrêa de Oliveira ambitiously argues the contrary. Drawing on papal and other classic sources, Professor Plinio Corrêa de Oliveira demonstrates the natural necessity of social hierarchy.
Plinio Corrêa de Oliveira, Nobility and Analogous Traditional Elites in the Allocutions of Pius XII: A Theme Illuminating American Social History (York, Penn.: The American Society for the Defense of Tradition, Family, and Property, 1993), Documents V, p. 481.
