In his article, the author claimed that studies of operant variability that use a lag-"n" or threshold procedure and measure the obtained variability through the change in U value fail to provide direct evidence that variability is an operant dimension of behavior. To do so, he adopted Catania's (1973) concept of the operant, which takes the increase in the overlap between an R distribution and an S distribution as the behavioral process that demonstrates an operant relation. This increase in overlap can be measured only if the reinforcement criterion and the measure of the effect of differential reinforcement are both defined on the same response property. Because the cited studies of operant variability defined their reinforcement criterion on a sequence property P and measured the effect of differential reinforcement on another sequence property P', their results cannot provide direct evidence that an operant relation was established. The commentators raised general points concerning (a) Catania's (1973) concept of operant; (b) the adequacy of applying Catania's concept to behavioral variability as an operant class; (c) the concept of differentiation and the role it plays in operant conditioning; (d) the possibility that more basic behavioral processes underlie the acquisition of behavioral variability in studies that measure variability in sequences of responses; and (e) the procedures and data of specific experiments designed to investigate operant variability. The points they raised led the author to see some aspects of his position that he had not yet considered and gave him a chance to clarify some aspects of his thesis. In this reply, the author will try to address the questions that the commentators have raised.