  Leibniz’s insistence that every individual substance has a complete concept entailed that, unlike Spinoza, he regarded Cartesian thinking substance and not Cartesian extended substance as paradigmatic of substance. Descartes’s extended substance (like Spinozistic substance) is, on Leibniz’s account, not a substance at all since it does not afford a principle of individuation. Leibniz argued that, whereas a real substance has a complete concept, the Cartesian notion of extended substance is an abstraction arrived at through an incomplete concept. Matter on its own is insufficient to form or to constitute a substance. For Leibniz, a body could never be a candidate for substance since bodies are susceptible to alteration and are infinitely divisible. We can thus never arrive at a body of which it can be said, “Here really is an entity.” Moreover, whereas Cartesian extended substance is totally inert, Leibniz insisted that activity is the hallmark of substance. Anything that acts is a substance; every substance constantly and uninterruptedly acts. For Leibniz, this position follows from God’s perfection. God’s planning of the universe was so perfect that it only required to be set in motion by him. True substances (that is, entia per se) are active and self-causing. On Leibniz’s account, God would lack all dignity were he the sole cause in the universe—that is, if occasionalism or interventionism were necessary. God’s perfect planning avoids the necessity for (continual or continuous) extraordinary concourse. Thus, God’s perfection entails that all substances are active; passive extension is only matter, not substance.