Amie Thomasson challenges advocates of layered conceptions of reality to explain “how layers are distinguished” and “what holds them together” by “examining the world” (2014). One strategy for answering such questions is mereological, treating inter-layer relations as parthood relations, where layers exist whenever composition does, and the number of layers will be equivalent to the number of answers to Peter Van Inwagen’s Special Composition Question, while answers to his General Composition Question explain what holds the layers together (1987). Various answers (...) have been proffered for these questions, from the physicalist atomism of Richard Feynman (2015), Hilary Putnam (1958), and Kit Fine (1992) to the holism of Jonathan Schaffer (2010), the two-layer emergentism of Van Inwagen himself (1995), Tim Maudlin’s three-layered “flash ontology” (2011), and Rob Koons two-layered “thermal substances” (2019). In this PhD project, I seek to meet Thomasson’s challenge by identifying which of these proposals are compatible with plausible interpretations of quantum physics. Atomist answers may have difficulty with relativity, while holistic and emergentist models have trouble giving an account of experimental conditions. Maudlin and Koons’ views, meanwhile, may make testable predictions about the scope of entanglement. Examining the world can lead us to sharply winnow our theories about how layers are distinguished and what holds them together. (shrink)