Full Idea
Functionalists deny that zombies are possible since states of mind (including conscious states) are purely functional states. If two agents are in the same functional state, regardless of qualitative difference, they are in the same mental state.
Gist of Idea
Functionalists deny zombies, since identity of functional state means identity of mental state
Source
John Heil (From an Ontological Point of View [2003], 20.5)
Book Reference
Heil,John: 'From an Ontological Point of View' [OUP 2005], p.247
A Reaction
In its 'brief' form this idea begins to smell of tautology. Only the right sort of functional state would entail a mental state, and how else can that functional state be defined, apart from its leading to a mental state?