the following line of reasoning, which is both different from Ross’s and by my lights
somewhat more compelling.^21 What defines the species in question are the differen-
tiating characteristic and the genus. In turn, what defines the differentiating charac-
teristic is whatever kinds it falls under as well as whatever features distinguish those
kinds from others in their genus. If the differentiating characteristic were to fall under
the genusbeing, thenbeingwould enter into the definition of the species of the genus
beingtwice: once by virtue of it being the genus that the species falls under, and a
second time by virtue of being part of what defines the differentiating characteristic
that is itself part of the definition of the species. But things can’t enter the same
definition twice over in this way.
These motivations potentially connect in interesting ways. For example, Aquinas
endorses Aristotle’s argument that being is not a genus, and uses that argument as the
basis for the claim that God falls under no genus. And the claim that God falls under
no genus is relevant to the question of whether there is any composition in God.^22 If
there is no composition in God, then God is maximally simple—and hence we have a
route to a theological motivation for ontological pluralism that is partially driven by
logical motivations.
The theological, phenomenological, and logical motivations for ontological plur-
alism are interesting and worthy of study. But none of these motivations fully
explain my attraction to ontological pluralism. My motivations are secular rather
than theological, more theoretical than phenomenological, and metaphysical rather
than logical (unless logic is conceived very broadly indeed). Ontological pluralism
promises to be a fruitful doctrine, potentially solving or at least ameliorating various
puzzles and problems that concern material objects, time, actuality and possibility,
the nature of ontological categories, ontological dependence and necessary connec-
tions more generally, the status of“negative entities”such as holes and shadows,
grounding, and essence.
I am interested in whether the fragmentation of being makes being a metaphys-
ician a little bit easier. It might be that some kinds of ontological pluralism do while
others do not, and for this reason I consider many versions of ontological pluralism
in the pages to come. I do not determine thefinal, best version of ontological
pluralism in the pages that follow; I fear that this task was too large for a single
book, or at least it proved to be too large for me to accomplish in a single book. The
reader should therefore be prepared for some unresolved tensions between the
theories that will be explored. My view is that we must approach metaphysics with
great humility. The questions are large and the considerations that might favor
(^21) Aquinas,Summa Contra Gentiles, book 1, chapter 25, section 6 (Aquinas 1991: 127). For further
commentary, see Alexander of Aphrodisias (1992: 142–6). See Aristotle’sTopicsVI.6, 144a27–b11
(Aristotle 1984a: 243) for Aristotle’s account of why, in general, differentiating characteristics can’t fall
under the genera they differentiate. 22
Aquinas,Summa Contra Gentiles, book 1, chapter 25, section 6 (Aquinas 1991: 127).