This thesis advances and defends a novel two-category ontology of objects and dimensions, latterly conceived as respects of comparability. The proposed 'dimensionist' ontology is set out (Chapter 1) and brought to bear on discussions of determinables and determinates (Chapter 2), the problem of universals (Chapter 3), fact ontologies (Chapter 4), and nomic governance (Chapter 5). Dimensionism is argued to fare well in comparison to a range of rival ontological accounts of property possession (Chapter 6). A metametaphysical framework is set out (Chapter 7) to undergird the discussion, which draws on both realist and pragmatist resources.