 The bottom level is usually thought to be at the smaller end of the spectrum: the atomistic view suggests that certain subatomic particles are fundamental. But this does not mean that the fundamental level must necessarily be at the bottom—the fundamental end could also be at the top, i.e., the universe as a whole could be considered fundamental—a substance in its own right (see Schaffer 2010b). Each of these views is a type of metaphysical foundationalism, which suggests that chains of ontological dependence must come to an end, at least at the dependent end. In other words, metaphysical foundationalism asserts that chains of asymmetric ontological dependence must terminate, they must be well-founded. The idea is typically formulated in mereological terms, as the reference to atomism suggests: there is an asymmetric ontological dependence relation from one end of the mereological scale to the other. These questions also have implications for the debate between pluralism and monism (one form of such monism is defended in Schaffer 2010b and Tallant 2015 discusses the notion of ontological dependence in connection to Schaffer’s monism; see also Trogdon 2009 and the separate entry on  monism).