Full Idea
Possibility could be just logical possibility (as involving no formal contradictions), or recombinations of all the existing elements (Armstrong), or truth in other concrete worlds (Lewis).
Gist of Idea
Possibility might be non-contradiction, or recombinations of the actual, or truth in possible worlds
Source
S.Mumford/R.Lill Anjum (Getting Causes from Powers [2011], 8.4)
Book Reference
Anjum,R.J./Mumford,S.: 'Getting Causes from Powers' [OUP 2011], p.179
A Reaction
All wrong, I would say. Well, avoiding contradiction is obviously a sense of 'possible'. Armstrong is wrong. It rules out new 'elements' being possible, and implies impossible combinations of the current ones. As for Lewis...