Full Idea
It seems logically possible that a creature physically identical to a conscious creature might have no conscious experiences (a zombie)…so conscious experience supervenes naturally but not logically on the physical.
Gist of Idea
Zombies imply natural but not logical supervenience
Source
David J.Chalmers (The Conscious Mind [1996], 1.2.1)
Book Reference
Chalmers,David J.: 'The Conscious Mind' [OUP 1997], p.38
A Reaction
"It seems possible" isn't much of an argument. This claim by Chalmers has been a great incentive to reassess what is or isn't possible. Can a brain lack consciousness? Can a tree fall over silently? Can cyanide stop poisoning us?