Abstract

The past thirty years has witnessed a resurgence of interest in 'realist ontologies': views that treat properties and relations realistically. Such views necessitate a metaphysical account of the structure of concrete particulars. One such account is the Substratum theory of concrete particulars, on which concrete particulars are composed of their properties together with a substratum that individuates them and bears these properties. A traditional objection to this account is that the substratum would be unknowable. Recently, several philosophers supporting a realist ontology have argued for versions of this traditional Substratum theory, insisting that this epistemic objection to the substratum can be overcome. I argue that this cannot be done. Specifically, I claim that either the substratum leads to a vicious regress or else it fails to meet epistemic constraints widely enforced in metaphysics. Therefore, realist ontologies must provide a Bundle theory of concrete particulars . ;Consequently, the traditional version of the Bundle theory, which construes properties to be universals, is assessed. The main objections that have been raised against this version of the theory are rejected; this includes what has been traditionally the most prominent objection, the charge that it is committed to the necessitation of the Identity of Indiscernibles. However, I also show that the theory requires applying the notion of bi-location to concrete particulars. I claim that this violates strong pre-theoretic intuitions about concrete particulars and renders the traditional Bundle theory inconsistent with a view attractive to contemporary realists, spacetime substantivalism. For these reasons, it is argued that the realist should adopt a Bundle theory that treats properties as tropes, rather than as universals. A Bundle theory formulated using tropes does not face the above limitations because it does not require the bi-location of concrete particulars. I also argue that the Bundle of tropes view has a further advantage over competing accounts of concrete particulars: it defuses the most serious theoretical obstacle to spacetime substantivalism: the notorious 'hole argument'.