 Yet Leibniz often seems to avert such a conclusion by appeal to his idea of “pre-established harmony”, and this is possible because he himself interprets this idea in two different ways. Early in his career, in such texts as “Primary Truths” (1680–84) and the “Discourse on Metaphysics” (1686) (both texts unpublished in Leibniz’s lifetime and not known to his immediate successors such as Wolff and Baumgarten), Leibniz introduces the doctrine of pre-established harmony on truth-theoretical grounds. His argument is that everything that is true of a substance is so because the predicate of a true proposition is contained in the complete concept of its subject and because that complete concept reflects the properties or “traces” in the substance that is that subject; that there are true propositions linking every substance in the world to every other, thus the complete concept of each substance must be a complete concept of the universe itself and each substance must bear within itself as properties traces of every other in the universe; and thus that each substance must reflect, or, as mental, represent the entire universe. Yet since (finite) substances are also defined as existing independently of one another (although not existing independently from the infinite substance, God), there is a question as to why each should truthfully represent all the others, which Leibniz answers by appeal to the idea of a pre-established harmony: although considered from the point of view of the concept of substance it does not seem necessary that every substance truly represent all the others, in his goodness, thus in his preference for a maximally harmonious world, God has nevertheless made it such that they do.