Subsequently, Skinner initiated a career of scientific investigation of behavior as a fundamental unit of analysis. Skinner (1931) attributed the concept of reflex to all living organisms, and defined it in a manner that related a response as a function of a stimulus, R = f(S). Skinner (1935) extended the function of individual stimuli and responses to classes, whose members are variations of each other but, nevertheless, have common functional effects. According to Skinner (1935), a class is generic in nature and "embraces an indefinitely large number of particular stimuli or responses but is sufficiently well defined by the specification of one or two properties" (p. 42). After defining the properties of a class, its membership is discovered by exploration (Skinner, 1938). Members may be added to the class as their common effects are observed.

Summary. Catania's definition of the generalized operant appears to rest largely on the concept of contingencies of different orders. Without this concept, the term generalized, as applied to operant classes, appears to be redundant. However, Catania has not yet specified the exact nature of these different orders of contingencies, and thus his definition of the generalized operant remains vague.