Full Idea
If one says that 'everything that exists is causally active', that rules out abstracta (notably sets and numbers), and it rules out objects that are causally isolated.
Gist of Idea
If all existents are causally active, that excludes abstracta and causally isolated objects
Source
Alexander Bird (Nature's Metaphysics [2007], 5.5)
Book Reference
Bird,Alexander: 'Nature's Metaphysics' [OUP 2007], p.114
A Reaction
I like the principle. I take abstracta to be brain events, so they are causally active, within highly refined and focused brains, and if your physics is built on the notion of fields then I would think a 'causally isolated' object incoherent.