My research so far has centered primarily on the notion of an object. Initially, I approached this topic from a semantic point of view, by investigating the mass/count distinction, a linguistic distinction found in an astonishingly wide range of languages between what is represented as countable (e.g., “chair”, “tree” and “people”) and what is represented only as measurable (e.g., “mud”, “air” and “sand”). In this area, I explored strategies by means of which mass terms can be accommodated within our familiar logical, semantic, and ontological apparatus, without forcing either the reduction of our mass-vocabulary to that of count nouns or the introduction of a mysterious category of “non-objects” or “stuff” to serve as the denotations of mass terms. The mass/count-distinction was the topic of my (unpublished) doctoral dissertation, Talk About Stuffs and Things: The Logic of Mass and Count Nouns (MIT, 1995) and continued to concern me in some of my subsequent publications, in particular “Isolation and Non-Arbitrary Division: Frege’s Two Criteria for Counting” (1997), “The Semantics of Mass-Predicates” (1999); “Genericity and Logical Form” (1999); “Review of Henry Laycock, Words Without Objects (2007) as well as “Nouns, Mass and Count” (2006), where I begin to apply some of the results of my subsequent work in metaphysics (see below) to this linguistic phenomenon.

The second area on which my work has focused concerns the more directly metaphysical question: What is an object? Many philosophers today find themselves in the grip of an exceedingly deflationary conception of what it means to be an object, according to which any plurality of objects, no matter how disparate or gerry-mandered, itself composes an object, even if the objects in question fail to exhibit interesting similarities, internal unity, cohesion or causal interaction amongst each other. My work, by contrast, attempts to develop a more full-blooded neo-Aristotelian approach, according to which objects are structured wholes: it is integral to the existence and identity of an object, on this conception, that its parts exhibit a certain manner of arrangement. This conception of parthood and composition is discussed in detail in my book, The Structure of Objects (Oxford University Press, 2008), which incorporates many of the ideas and the broader perspective tested out in “The Crooked Path from Vagueness to Four-Dimensionalism” (2003), “Constitution and Similarity” (2004), “Almost Indiscernible Objects and the Suspect Strategy” (2005), “On the Substantive Nature of Disagreements in Ontology” (2005), “Towards a Neo-Aristotelian Mereology” (2006), “Aristotle’s Mereology and the Status of Form” (2006), as well as “Review of Theodore Sider, Four-Dimensionalism: An Ontology of Persistence and Time (2003) and “Review of Verity Harte, Plato on Parts and Wholes: The Metaphysics of Structure (2004).

In my current work, I continue my defense of a hylomorphic conception of concrete particular objects as compounds of matter (hulē) and form (morphē or eidos).  My new book, entitled Form, Matter, Substance (Oxford University Press, 2018), argues that a hylomorphic analysis of concrete particular objects is well equipped to compete with alternative approaches when measured against a wide range of criteria of success. A successful application of the doctrine of hylomorphism to the special case of concrete particular objects, however, hinges on how hylomorphists conceive of the matter composing a concrete particular object, its form, and the hylomorphic relations which hold between a matter–form compound, its matter and its form. Through the detailed answers to these questions developed in this book, matter–form compounds, despite their metaphysical complexity, emerge as occupying the privileged ontological status traditionally associated with substances, due in particular to their high degree of unity.  This work pulls together, and develops further, the various components of this approach discussed separately in “Essence, Necessity and Explanation” (2012), “Varieties of Ontological Dependence” (2012), “Ontological Dependence: An Opinionated Survey” (2013), “Substance, Independence and Unity” (2013), “The Causal Priority of Form in Aristotle” (2014), “The Coarse-Grainedness of Grounding” (2015), “Where Grounding and Causation Part Ways: Comments on Jonathan Schaffer” (2015), “In Defense of Substance” (2015), “Questions of Ontology” (2016), “Essence and Identity” (2018), and "Towards a Hylomorphic Solution to the Grounding Problem" (2018).