Full Idea
Functionalism is a new incarnation of behaviourism, replacing sensory inputs with sensory inputs plus mental states, and replacing dispositions to act with dispositions plus certain mental states.
Gist of Idea
Functionalism is behaviourism, but with mental states as intermediaries
Source
Ned Block (Troubles with Functionalism [1978], p. 69)
Book Reference
'The Philosophy of Mind', ed/tr. Beakley,B /Ludlow P [MIT 1992], p.69
A Reaction
I think of functionalism as behaviourism which extends inside the 'black box' between stimulus and response. It proposes internal stimuli and responses. Consequently functionalism inherits some behaviourist problems.