Could we learn something similar aboutexistence? We can wrap our heads around
the idea that existence is a property (eitherfirst- or second-order), but could
existence be arelation? And, if so, what could the relata possibly be?
The material objects with which we are most familiar exist at some times rather
than others. The abstract objects that populate Plato’s heaven—such asmathematica
and their ilk—do not exist at any time at all, but rather exist atemporally. Let us
explore a view that takes these statements at face value, one according to which the
kind of existence enjoyed by material things is literallyrelative to a timewhereas
the kind of existence enjoyed by abstract objects is not. On such a view,existenceis
a systematically variably polyadic feature: when restricted to one category, it is a
relation to a time, when restricted to another, it is a monadic property.
On this view, for a material object to be at a time is for it to literally exist at that
time. For a material objectto beit mustbe at some time or other. The kind of
existence enjoyed by a material being is existence relative to a time.
One frequently sees the phrase“exists at a time”in the literature on persistence
through time. This expression is extremely common. To see this, simply search, via
an Internet search engine,“exists at a time”. (Note that I used it myself in the second
paragraph of this subsection. Did you even bat an eye?) Now one could hold that the
phrase is extremely misleading, and that it would be better to say that an object is
locatedat a time rather than that itexistsat a time. But one is not required to say this.
The fact that“exists at a time”and similar locutions have enjoyed such currency
among metaphysicians and ordinary people suggests that they are perspicuous. The
view described here takes them at face value.
This view also receives support from metaphysical considerations. Material objects
are necessarily temporal. It is hard to see what could ground this necessity if the
locationrelation is metaphysically distinct fromexistence. On this alternative hypoth-
esis, there are material objects and there are times, and there is a metaphysically
primitive relation linking the two.^29 On this hypothesis, it is not at all clear why any
material object must bear this relation to some time or other. I suspect that it is
this view of the relation of material objects to times that has led some philosophers to
take seriously the claim that material objects could exist in worlds without time. For
example, Sider (2001: 99–101) presents an argument that takes this putative possi-
bility as a premise and has as its conclusion the view that material objects cannot
persist through time via enduring. However, there is no mystery if what it is for a
material object to be is for it to be at some time. It is part of the very being of a
material being that it is in time, and hence timeless worlds of the sort Sider envisions
are impossible. This response to Sider does presuppose that objects necessarily enjoy
the mode of being they actually enjoy provided that they enjoy any mode of being at
all. We’ll subject this presupposition to greater scrutiny in chapters 3 and 9, but for
(^29) See Gilmore (2007), Hudson (2005), and McDaniel (2006a, 2007) for explications of this picture.