For the mature Leibniz, a living being is a created substance composed of an infinitely complex organic body and a simple, immaterial soul. Soul and body do not interact directly, but rather their states correspond according to a harmony preestablished by God. I show that Leibniz’s theory faces challenges with respect to the question of whether substances need to possess knowledge of how they bring about their effects, and I argue that, to address these challenges, Leibniz turns to a concept (...) of “divine preformation” that he attributes to both soul and body. Insofar as divine preformation provides Leibniz with an explanation for how soul and body can both act without possessing explicit knowledge of what they are doing, it serves as a key tool for justifying the theory of preestablished harmony. (shrink)