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 ab