H. P. Grice, "Response and Respondent"

Skinner's behavioral theory was largely set forth in his first book, Behavior of Organisms (1938).[9] Here, he gives a systematic description of the manner in which environmental variables control behavior. He distinguished two sorts of behavior which are controlled in different ways:  Respondent behaviors are elicited by stimuli, and may be modified through respondent conditioning, often called classical (or pavlovian) conditioning, in which a neutral stimulus is paired with an eliciting stimulus. Such behaviors may be measured by their latency or strength. Operant behaviors are 'emitted,' meaning that initially they are not induced by any particular stimulus. They are strengthened through operant conditioning (aka instrumental conditioning), in which the occurrence of a response yields a reinforcer. Such behaviors may be measured by their rate. Both of these sorts of behavior had already been studied experimentally, most notably: respondents, by Ivan Pavlov;[25] and operants, by Edward Thorndike.[26] Skinner's account differed in some ways from earlier ones,[27] and was one of the first accounts to bring them under one roof.