Abstract: It is known that the doctrine of property as an individual natural right expounded in the Encyclical Rerum Novarum (1891) is Lockean more than Thomistic. Locke’s thought provided a convenient shield against the Church’s new enemy, Socialism. But the Church had also to face her own newly rediscovered tradition, dating back to Gratian’s Decree: natural law prescribed the commonality of natural resources, human law instituted private property. Rerum Novarum had two options: (i) to sterilize the “scholastic tradition” through a reductive interpretation, or (ii) to shift to an altogether different (Lockean) theory. It is shown that in its uneasiness it cannot choose. No consistent theory of appropriation can be found in the Encyclical.