Full Idea
If any characterization of the abstract deserves to be regarded as the modern standard one, it is this: an abstract entity is a non-spatial (or non-spatiotemporal) causally inert thing. This view presents a number of perplexities...
Gist of Idea
Nowadays abstractions are defined as non-spatial, causally inert things
Source
Gideon Rosen (Abstract Objects [2001], 'Non-spat')
Book Reference
'Stanford Online Encyclopaedia of Philosophy', ed/tr. Stanford University [plato.stanford.edu], p.3
A Reaction
As indicated in other ideas, the problem is that some abstractions do seem to be located somewhere in space-time, and to have come into existence, and to pass away. I like 'to exist is to have causal powers'. See Ideas 5992 and 8300.
Related Ideas
Idea 5992 Chrysippus says action is the criterion for existence, which must be physical [Chrysippus, by Tieleman]
Idea 8300 Perhaps possession of causal power is the hallmark of existence (and a reason to deny the void) [Lowe]