“…In spite of this, and though the rationale for doing so may be neither crystal-clear nor consistently applied, private events have been singled out by behavior analysts as being second-rate stimuli, in the sense that they cannot be full and real causes of behavior. This appears problematic, because an explanation seems to be lacking as to why internal stimuli , whose status is said to be "identical to that of any other aspect of the physical world" (Delprato & Midgley, 1992, p. 1512, are still assumed to lack the capacity to cause behavior in the same full sense as stimuli that can be more easily observed.…”