Jonathan Schaffer

Schaffer advocates a neo-Aristotelean approach to Ontology in which existence questions are largely trivial. Composite objects, abstract objects, fictional characters, and many other philosophically contentious entities exist. Rather than debating such objects' existence, the primary role of metaphysics is to organize all existent entities into a hierarchical dependence structure. Within this structure, all existing things are classified as fundamental entities, derivative entities, or grounding relations.[8]

Fundamental entities (also called substances) have nothing ontologically prior to them upon which their existence depends. They are the most basic units of existence. Derivative entities, on the other hand, depend upon other entities for their existence. Schaffer uses the holes in a block of Swiss Cheese as an example of a derivative entity, since the holes are ontologically dependent upon the cheese. A derivative entity may be grounded in either another derivative entity or in a substance. A grounding relation is a primitive relation of dependence that holds between a derivative entity and that entity's "grounds". Grounding relations are irreflexive, asymmetric, and transitive.[8] This allows for chains of grounding. Schaffer asserts that all chains of grounding must terminate in a fundamental entity in his "well-foundedness" assumption. [9]

Schaffer is perhaps most well-known for his arguments in favor of Priority Monism. Priority Monism is a form of Monism that claims that while very many entities exist, only one is fundamental. For Schaffer, this entity is the cosmos. Schaffer's position is motivated by his belief that the whole universe may be an entangled system and thus have properties that are not reducible to the universe's parts. "Monism: The Priority of the Whole"[9] also contains his Argument from Gunk, according to which mereological atoms cannot be fundamental due to the possibility of infinitely divisible matter.