 It is hard to tell why Leibniz is troubled by any theory that involves the potential loss of causal efficacy in substances. Part of it might have to do with his belief that even finite, created substances are naturally indestructible (i.e., immortal) (Principles of Nature and Grace §2 GP vi, 598/P 195). For then created, finite substances, continually acting according to the physical influx model, might eventually lose their causal efficacy and would no longer be able to act. And for Leibniz, “substances cannot be conceived in their bare essence, devoid of activity; that activity is of the essence of substance in general” (New Essays A vi, 6, 65). So, physical influx would entail the natural mortality of substance, a view that Leibniz wholly rejects.