  Although objects and universals are typically included along with  facts in the basic ontology of combinatorialism, facts are typically  considered more fundamental. Indeed, taking his queue from the  Tractarian thesis that the world consists of facts, not things,  Armstrong (1986a, 577) argues that facts alone are ontologically  basic and that objects and universals are simply “aspects of,  abstractions from” facts. Accordingly, he calls the object  constituent of a fact of the form [P,a] a  “thin” particular, an object “considered in  abstraction from all its [intrinsic] properties” (1993, 433);  and where N is the conjunction of “all the non-relational  properties of that particular (which would presumably include  P), the atomic fact a's exemplifying N itself is the  corresponding “thick” particular ” (ibid.,  434 — we will occasionally use italics to distinguish a thin  particular a from the corresponding thick particular  a). Though not all combinatorialists of every stripe buy into  Armstrong's “factualist” metaphysics (Bricker 2006), they do generally agree that facts are more fundamental, at least to the  extent that both the notion of a bare particular, i.e., an object  exemplifying no properties, and that of an unexemplified property are considered incoherent; insofar as they exist at all, the existence of both particulars and universals depends on their  “occurring” in some fact or other. Whatever their exact  ontological status, it is an important combinatorialist thesis that  exactly what objects and universals exist is ultimately a  matter for natural science, not metaphysics, to decide. 