Full Idea
Functionalism seems to commit us to bizarre possibilities, such as 'zombies'.
Clarification
'Zombies' have conscious behaviour, but no conscious states
Gist of Idea
Functionalism commits us to bizarre possibilities, such as 'zombies'
Source
E.J. Lowe (Introduction to the Philosophy of Mind [2000], Ch. 3)
Book Reference
Lowe,E.J.: 'Introduction to the Philosophy of Mind' [CUP 2000], p.67
A Reaction
This goes with the tendency of functionalism to imply epiphenomenalism - that is, to make the intrinsic character of mental states irrelevant to thinking. I'd love to eavesdrop on two zombies in an art gallery.