The four principal competing substance ontologies are substratum theory, bundle theory, primitive substance theory, and hylomorphism. Both historically and in the recent literature, most arguments pertaining to these four theories have been developed under the assumption that only one of them can be true. However there is room in this debate for various forms of pluralism: mild pluralism here refers to the view that while only one of these four theories is true of our world, there is at least one (...) other possible world in which a different substance ontology obtains; moderate pluralism refers to the view that while only one of these four theories is true of our world, there is at least one other possible world in which multiple substance ontologies obtain ; and extreme pluralism refers to the view that our own actual world contains substances belonging to different substance ontologies. In this paper I lay out a novel argument for a version of extreme pluralism. (shrink)