It has become customary in modern behavioristics to speak of stimuli as though they elicit responses from organisms. But logically this is absurd, for analysis of the grammatical roles of stimulus and response concepts shows that stimuli and responses differ in logical type from causes and effects. The “S elicits R” formula thus stands revealed as elliptical for a more complicated form of assertion. The trouble with this ellipsis, however, is that by suppressing vital components of formal structure in behavioral principles, it has led to gratuitous assumptions about the environmental antecedents of behavior and seriously undermined the ability of behavior theory to assimilate the “higher mental processes.”