Leibniz’s major works include The Monadology (1714), Discourse on Metaphysics (1686), Theodicy (1710), and The Leibniz-Clarke Correspondence (1714–1715), as well as political writings and a large body of unedited material. Leibniz had a very complex view of the universe that defied common sense, was theoretically fascinating, and preserved core Christian beliefs. His philosophical writings were highly complex and had their own terminology. He claimed that his philosophy was based on these general principles: principle of identity, principle of the best, principle of sufficient reason, metaphysically necessary principles, principles of order, principles of causation, and the principle of the natural. In addition to this, he used the idea of monads as the basic unit of what was real.