In this response to Skinner's criticism of a previously written article, Herrnstein notes that phylogenic behavior as used by Skinner refers to a third kind of behavior. Herrnstein suggests that this is neither a necessary nor a desirable addition to behavioristic analysis. (Author/AM)

Although reinforcement often leads to repetitive, even stereotyped responding, that is not a necessary outcome. When it depends on variations, reinforcement results in responding that is diverse, novel, indeed unpredictable, with distributions sometimes approaching those of a random process. This article reviews evidence for the powerful and…

A condensed review of the concepts of exploration and play is presented, followed by an outline of the major research findings. From this basis, gaps in the literature and new research directions are discussed. (Author/AM)

Results suggest that adults may not be able to discover-invent-produce the learning that is necessary to behave more effectively; that they may be unaware of this possibility; and that if they try to get help from well intentioned others, it will tend to make things worse. (Author/AM)