Full Idea
B-properties logically supervene on A-properties if no two logically possible situations are identical with respect to their A-properties but distinct with respect to their B-properties.
Gist of Idea
Logical supervenience is when one set of properties must be accompanied by another set
Source
David J.Chalmers (The Conscious Mind [1996], 1.2.1)
Book Reference
Chalmers,David J.: 'The Conscious Mind' [OUP 1997], p.35
A Reaction
This is the gap into which Chalmers wants to slip zombies. He's wrong. He thinks that because he can imagine Bs without As, that this makes their separation logically possible. No doubt he can imagine a bonfire on the moon.