Gottfried Wilhelm Leibniz, a prominent figure in modern Western philosophy, developed the concept of pre-established harmony as a central feature of his metaphysical system. This idea emerges primarily from his attempts to reconcile the apparent interaction between mind and body, and more broadly, to explain the coordination and order observed in the universe. In Leibniz’s philosophy, monads—simple, indivisible, and immaterial substances—constitute the ultimate building blocks of reality. Each monad is self-contained and reflects the universe from its own perspective, possessing no causal influence on other monads directly. This raises a profound philosophical problem: how can monads exhibit coherent interaction if they are causally independent? Leibniz resolves this dilemma through his doctrine of pre-established harmony. Pre-established harmony posits that God, in the act of creation, synchronized all monads in advance so that their internal developments correspond perfectly with each other. In other words, the apparent interaction between mind and body, or among any substances, is not the result of causal influence, but the result of a divinely orchestrated correspondence. For instance, when a person decides to lift their arm, it seems as though the mental decision causes the physical movement.