We speak of operant behaviour as emitted because the main variable controlling the frequency of the performance is the way in which the performance changes the environment. The emitted nature of operant behaviour is to be contrasted with the elicited nature of reflex behavior. In operant behaviour the main emphasis is on the stimulus which follows the performance in contrast to reflex behaviour where the main emphasis is on the stimulus which precedes the response and elicits or evokes it. Because operant behaviour is emitted, it has the quality of purposiveness, in contrast to the highly determined nature of the reflex.