Full Idea
For some metaphysicians, possession of causal power is the very hallmark of real existence (and is one reason, for instance, why some have denied the existence of the void or absolute space).
Gist of Idea
Perhaps possession of causal power is the hallmark of existence (and a reason to deny the void)
Source
E.J. Lowe (The Possibility of Metaphysics [1998], 10.2)
Book Reference
Lowe,E.J.: 'The Possibility of Metaphysics' [OUP 2001], p.213
A Reaction
You could try saying that space has the power of making movement possible. The 'hallmark' of something doesn't define what it is. Existence without causal power seems logically possible and imaginable, but unlikely. Epiphenomena have this problem.