 Desgabets’s thesis concerning the indefectibility of created substances, which underlies his metaphysics, is perhaps his most original if not radical philosophical contribution (Schmaltz, 2002; Easton, 2005; Gatto, 2017). Gatto argues that this thesis is the key to understanding Desgabets’s peculiar development of Descartes’s philosophy (Gatto, 2017). In a letter from Desgabets to Malebranche, we learn that he had begun the Treatise on the Indefectibility of Substances, as early as 1649 (Letter from Desgabets, Sept. 1674, Malebranche, 1958–84, vol. II: 85). It was Desgabets’s view that substances, in their essence and existence, are eternal, indivisible, immutable, and indestructible, which is to say, indefectible. While the modes of substance can undergo change, the essence of substance and its existence cannot. According to Desgabets, the indestructibility, eternality, and indivisibility of substances follow from the fact that God created substances by a free and indifferent will. Once the world was created, it could not be uncreated. Thus, the key to understanding Desgabets’s indefectibility thesis lies not only in his analysis of the Cartesian doctrine of substance, but in his interpretation of Descartes’s notoriously opaque doctrine of the free creation of the eternal truths, discussed in a later section, under “Truth.” 