 Even worse, Spinoza faces an especially thorny problem in justifying (16). For his account of the concept of God in (15) relies on commitments that even those friendly to theism, such as Descartes, would surely reject. Spinoza defines God in Id6 as “a substance consisting of an infinity of attributes, of which each one expresses an eternal and infinite essence.” Spinoza claims in Ip9, without any explicit argument, “The more reality or being each thing [unaquaeque res] has, the more attributes belong to it.” This definition of God and the supporting principle in Ip9 were controversial even in Spinoza’s own day. According to Descartes, a substance cannot have more than one (principal) attribute.[5] To say that the concept of God is the concept of a substance with multiple (principal) attributes is, in fact, to appeal to an internally inconsistent concept. So, the objection runs, not only has Spinoza failed to justify (16), but (15) is outright false.