Full Idea
A non-actual state of affairs in possible if there actually was a substance capable of initiating a causal chain, perhaps non-deterministic, that could lead to the state of affairs that we claim is possible.
Gist of Idea
States of affairs are only possible if some substance could initiate a causal chain to get there
Source
Jonathan D. Jacobs (A Powers Theory of Modality [2010], §4.2)
Book Reference
-: 'Philosophical Studies' [-], p.12
A Reaction
[He is quoting A.R. Pruss 2002] That seems exactly right. Of course the initial substance(s) might create a further substance, such as a transuranic element, which then produces the state of affairs. I favour this strongly actualist view.