  Historically the distinction between abstract and concrete objects has been thought of as exclusive and exhaustive. But the exhaustiveness of the distinction has recently been questioned. Linsky and Zalta argue that while abstract objects are necessarily abstract, there are objects which are not concrete but could have been concrete. These objects are non-concrete in virtue of being non-spatiotemporal and causally inert but they are not abstract since they could have been concrete (Linsky and Zalta 1994). Since Nominalism rejects abstract objects because of their non-spatiotemporality and their causal inertness, Nominalism also rejects non-concrete objects.