Skinner's views are commonly misrepresented. One reason for this difficulty is that changes in the way that Skinner formulated his views occurred in a gradual evolution over time throughout Skinner's career, and the changes and their significance were not as conspicuously marked as they might have been. Among these changes were a movement from a two-term necessity to a three-term contingency; a movement from discriminative stimulus to setting as the first term in his three-term contingency; and a movement from determinism to random variation as a foundational principle in his selectionist behaviorism. When not seen in their historical development over time, a sample reading of Skinner's views may readily result in misleading or inaccurate interpretations, particularly in respect to his later work. Seen in historical context, however, the accounts that survived after the changes Skinner made are well integrated in a selectionist theory of behavior.