  The characterisation of abstract objects as non-spatiotemporal and causally inert objects might be thought unsatisfactory to the extent that it tells us only what they are not, but not what they are. But this is not a problem for the nominalist. The business of the nominalist is to reject such objects, not to characterise them in a positive way. And for the purposes of rejecting abstract objects, their characterisation as non-spatiotemporal, causally inert objects is a reasonably clear characterisation (at least as clear as the notions of spatiotemporal object, causation, causal power, and related ones are).