  For Leibniz, at the most fundamental level, reality is characterized by simple substances, or “monads”, a term that Leibniz picked up from Francis Mercury van Helmont and Anne Conway in 1696 (Merchant 1979). Since there are composites, Leibniz argued, there must be simple substances that, together, constitute these composites. Being simple, monads have neither parts, nor extension, nor form, nor divisibility. Leibniz saw them as the “true Atoms of nature”. While Leibniz thus retained a strong commitment to substance, he resisted rationalism’s synechistic momentum, which privileged the metaphysical and methodological stance of the continuity of the universe, by rehabilitating substance’s Aristotelian role as an individuator. However, while, for Aristotle, Bucephalus is a proper substance, Leibniz regarded Bucephalus not as a substance but as himself comprising a collection of simple substances. Leibniz agreed with Aristotle’s characterization of substance as the grammatical subject of predication and not itself predicable of anything else. However, he complained that this account does not go far enough. For Leibniz, the essence of substance lies not in the fact that it is the subject of predication, but in the fact that every possible predicate may be asserted or denied of it. In this way, every individual substance has a complete concept, a conception so complete (that is, so fully determinate) that every fact about the substance, and about its situation in the universe—past, present or future —follows from it analytically.