Full Idea
Behaviourists had trouble providing a robust construal of mental causation (and hence had no logical space for a psychology of mental processes).
Clarification
A 'contrual' is an explanation
Gist of Idea
Behaviourism has no theory of mental causation
Source
Jerry A. Fodor (Psychosemantics [1987], p. 67)
Book Reference
Fodor,Jerry A.: 'Psychosemantics' [MIT 1993], p.67
A Reaction
If they could reduce all mental events to stimulus-response, that seems to fall within the normal procedures of physical causation. There is no problem of mental causation if your ontology is entirely physical.