Verbal Behavior: Extended Edition. Chapter 19: Thinking. Quote 32

Tradition and expedience seem to agree in confining the analysis of human thought to operant behavior. So conceived, thought is not a mystical cause or precursor of action, or an inaccessible ritual, but action itself, subject to analysis with the concepts and techniques of the natural sciences, and ultimately to be accounted for in terms of controlling variables. (p. 449)