Full Idea
Where properties are possessed by all kind members, we must distinguish the accidental from essential ones by considering all actual and possible kind members.
Gist of Idea
To distinguish accidental from essential properties, we must include possible members of kinds
Source
Stephen Mumford (Laws in Nature [2004], 07.5)
Book Reference
Mumford,Stephen: 'Laws in Nature' [Routledge 2006], p.117
A Reaction
This is why we must treat possibilities as features of the actual world.