Full Idea
Functionalism has three distinct levels of description: a neurophysiological description, a functional description (relative to a program which the brain is realising), and it may have a further mental description.
Gist of Idea
Functionalism has three linked levels: physical, functional, and mental
Source
William Lycan (Introduction - Ontology [1999], p.6)
Book Reference
'Mind and Cognition (2nd Edn)', ed/tr. Lycan,William [Blackwell 1999], p.6
A Reaction
I have always thought that the 'levels of description' idea was very helpful in describing the mind/brain. I feel certain that we are dealing with a single thing, so this is the only way we can account for the diverse ways in which we discuss it.