  Part of Leibniz’s motivation for holding to pre-established harmony was the alleged impossibility of making sense of transeunt causation—that is, causation understood as a direct relation between distinct monads (as opposed to immanent causation, which holds between successive stages of a monad’s life). If direct interaction is impossible, how to account for the correlations between things except by assuming that it had been established by a supreme Architect? In the hands of Leibniz, this surprising view as to the nature of causation becomes the foundation of an original proof of God’s existence.