Full Idea
The functionalists' point is that higher-level properties like being in pain or computing the sum of 7 and 5 are not to be identified with ("reduced to") or mistaken for their realisers.
Gist of Idea
Functionalists emphasise that mental processes are not to be reduced to what realises them
Source
John Heil (Philosophy of Mind [1998], Ch.4)
Book Reference
Heil,John: 'Philosophy of Mind' [Routledge 1998], p.94
A Reaction
I take it that functionalist minds can't be reduced because they are abstractions rather than physical entities. Nevertheless, the implied ontology seems to be entirely physical, and hence in some sense reductionist.