be an ontological category. Is this because it is not generalenough? So the cut-off
problem remains.
The cut-off problem is serious and Westerhoff (2005) nicely demonstrates how it
problematizes most of the accounts he discusses. Although a plausible account of
ontological categories will most likely appeal to the notion of naturalness, it seems
that it must appeal to other notions as well. (It is clear, for example, that the identity
account roughly characterized earlier in this section suffers from the cut-off
problem.)
4.4 Ontological Categories as Ways of Being
It’s tempting to gloss ontological pluralism as the doctrine that different ontological
categories correspond to different ways of being. But why have two notions? Perhaps
ontological categories just are ways of being. In which case, two things belong to the
same ontological category if and only if they exist in the same way. Two things exist
in the same way if and only if they are in the domain of the same perfectly natural
quantifier.
The account of ontological categories as ways of being is a traditional view.
Aquinas (1993: 53) seems to endorse this view when he writes that,
... existing can have different levels which correspond to different ways of existing and define
different categories of thing. Thus, a substance is not some sort of generic existent differen-
tiated by adding a certain nature, but the wordsubstanceexpresses a special way of existing.
In this passage, Aquinas explicitly equates the“categories of things,”i.e., ontological
categories, with the different levels of existing that correspond to the different
ways of being.^28 On his view, we shouldn’t think of the category of substance as
simply a highly natural kind of entity: kinds are“generics”differentiated by adding
a certain nature. Rather the word“substance,”understood as the name of a category,
purports to stand for a specific mode of existing. And in general, the categories
correspond to the modes of being.^29 As Aquinas says here, they“define different
categories of thing.”^30
(^28) The theory defended here makes no use of the notions of levels, orders, or grades of being, although it
is consistent with levels and orders of being corresponding to categorial differences. We’ll have more to say
about grades of being in chapters 5 and 7. Brower (2014: 49, 219–22) argues that Aquinas is committed to
even more modes of being than those that Aquinas calls categories, but grants that, for Aquinas, the
categories do correspond to modes of being. See also Galluzzo (2014: 218 29 – 19).
30 Knuutila (2012: 71) notes that Aquinas associates categories with modes of being.
On Aquinas’s view, there is a being, God, who does not belong to any of the ten categories recognized
by Aristotle. But also on Aquinas’s view, God enjoys a mode of being that is distinct from the mode of being
of any entity within the ten categories. (God in fact enjoys being identical with His mode of being.) As it
were, God is the sole member of the ontological category to which He belongs (and is identical with).
Pasnau and Shields (2004: 61) note that, for Aquinas, strictly God is not a substance; see also Brower (2014)
and Stein (2009: 7).