 For Leibniz, a world of genuinely active substances is more perfect than a world of purely passive or causally inert substances, whose activity is not properly ascribed to them but to God. Ascribing such activity to God alone, Leibniz believes, leads inexorably to Spinozism, where God is the only real substance and where any other thing is just a mode of God or else must invoke a deus ex machina, which for Leibniz is an ad hoc solution (Primary Truths C 521/P 90; GP iv, 515/WF 221). In order to avoid what he thinks is unadulterated Spinozism, Leibniz is keen to emphasize that we must be able to distinguish the actions of God from the actions of created substances. (The success of this endeavor of Leibniz’s is debatable, as discussed in the section on divine causation.)