  It should be noted that Skinner’s views about explanation and the purported circularity of explanation by reference to inner processing are both extreme and scientifically contestable, and that many who have self-identified as behaviorists including Guthrie, Tolman, and Hull, or continue to work within the tradition, broadly understood, including Killeen (1987) and Rescorla (1990), take exception to much that Skinner has said about explanatory references to innerness. Also Skinner himself is not always clear about his aversion to innerness. Skinner’s derisive attitude towards explanatory references to mental innerness stems, in part, not just from fears of explanatory circularity but from his conviction that if the language of psychology is permitted to refer to internal processing, this goes some way towards permitting talk of immaterial mental substances, agents endowed with contra-causal free will, and little persons (homunculi) within bodies. Each of these Skinner takes to be incompatible with a scientific worldview (see Skinner 1971; see also Day 1976). Finally, it must be noted that Skinner’s aversion to explanatory references to innerness is not an aversion to inner mental states or processes per se. He readily admits that private thoughts and so on exist. Skinner countenances talk of inner events but only provided that their innerness is treated in the same manner as public behavior or overt responses. An adequate science of behavior, he claims, must describe events taking place within the skin of the organism as part of behavior itself (see Skinner 1976). “So far as I am concerned,” he wrote in 1984 in a special issue of Behavioral and Brain Sciences devoted to his work, “whatever happens when we inspect a public stimulus is in every respect similar to what happens when we introspect a private one” (Skinner 1984b, p. 575; compare Graham 1984, pp. 558–9).