In his “Tactics of Scientific Research” (1960), his work on avoidance, his discovery of equivalence classes and his cautions on applications of coercion, Murray Sidman created high standards for behavior analytic research. I illustrate his influence in the context of three examples he might have characterized as pilot studies. Each examined trial N+1 response probabilities depending on whether trial N responding had produced a reinforcer. Differentially reinforced interresponse times, keys pecked in arbitrary matching, and two‐key response sequences provided no robust evidence that reinforcing some response property on trial N raises the probability of responding with that property on trial N+1. These negative findings shed light on the nature of operant classes and on the relation of reinforcers to the responses that produced them. Through selection, reinforcers create operant classes and engender variations of the responses within those classes; operant classes are held together by common contingencies. Sidman extended our understanding of operant classes by expanding them to include equivalence relations.