 In the remainder of this subsection, we focus on the first criterion in the above proposal, namely, the non-spatial condition. But it gives rise to a subtlety. It seems plausible to suggest that, necessarily, if something \(x\) is causally efficacious, then (since \(x\) is a cause or has causal powers) \(x\), or some part of \(x\), has a location in time. So if something has no location in time, it is causally inefficacious. The theory of relativity implies that space and time are nonseparable, i.e., combined into a single spacetime manifold. So the above proposal might be restated in terms of a single condition: an object is abstract if and only if it is non-spatiotemporal. Sometimes this revised proposal is the correct one for thinking about abstract objects, but our discussion in the previous section showed that abstract artifacts and mental events may be temporal but non-spatial. Given the complexities here, in what follows we use spatiotemporality, spatiality, or temporality, as needed.