Discourse on MetaphysicsGottfried Wilhelm Leibniz

Written in 1686 but unpublished in Leibniz's lifetime, the Discourse on Metaphysics is the first mature statement of his philosophical system. In thirty-seven short sections, Leibniz lays out the core ideas that would occupy him for the next three decades: the complete concept of an individual substance, pre-established harmony, the identity of indiscernibles, and the claim that God has created the best of all possible worlds.

Every individual substance, Leibniz argues, contains in its complete concept the whole series of its predicates, past, present, and future. Caesar's crossing of the Rubicon is contained in the concept of Caesar just as surely as his birth. This makes each substance a mirror of the entire universe from its own perspective. God, in creating, chooses from infinitely many possible worlds the one that maximizes perfection, where perfection means the greatest variety of phenomena governed by the simplest laws.

The Discourse also takes aim at both Cartesian mechanism and the Scholastic reliance on substantial forms. Leibniz insists that force, not extension, is the essence of body, and that something like Aristotelian form must be preserved in physics if we are to explain the unity and activity of substances. The work sets the agenda for the Monadology and the Theodicy, compressing into a few pages the metaphysical architecture that the later works elaborate.