Full Idea
A central tenet of functionalism is that objects can be dispositionally indiscernible but differ qualitatively as much as you please.
Clarification
A 'tenet' is a basic opinion
Gist of Idea
Functionalists say objects can be the same in disposition but differ in quality
Source
John Heil (From an Ontological Point of View [2003], 11.3)
Book Reference
Heil,John: 'From an Ontological Point of View' [OUP 2005], p.115
A Reaction
This refers to the multiple realisability of functions. Presumably we reconcile essentialism with the functionalist view by saying that dispositions result from combinations of qualities. A unique combination of qualities will necessitate a disposition.