Descartes notoriously characterizes substance in two ways: first, as an ultimate subject of properties ; second, as an independent entity. The characterizations have appeared to many to diverge on the definition as well as the scope of the notion of substance. For it is often thought that the ultimate subject of properties need not—and, in some cases, cannot—be independent. Drawing on a suite of historical, textual, and philosophical considerations, this essay argues for an interpretation that reconciles Descartes's two characterizations. It (...) proposes that both characterizations invoke a type of independence that obtains just in case there is no relation to another entity that holds by the nature of the entity in question. Even though the ultimate subject of properties is sometimes not independent in other respects, it satisfies this independence-by-nature condition. (shrink)