In previous studies, researchers have attempted to generate learning hierarchies using task analysis based primarily on epistemological considerations (Gagné & Paradise, 1961; Gagné, 1962; Cox & Graham, 1966; Uprichard, 1970; Okey Gagne, & 1970; Harke, 1971; Riban, 1971; Phillips & Kane, 1973; Miller & Phillips, 1975). Studies of this type conducted in the early si xties provide substantial evidence to support the hierarchical structureofknowledge(Gagné & Paradise, 1961;Gagné & Brown, 1961:Gagné, 1962, 1963; Gagné, Mayor, Garstens, & Paradise, 1962; Gagné & Staff, 1965). An examination of results from recent studies (Niedermeyer, Brown, & SulLen, 1969; Brown, 1970; Phillips & Kane, 1973; Callahan & Robinson, 1973) suggests that optimal learning sequences can be developed by sequencing instructional materials according to validated learning hierarchies. However, both Gagné (1968) and Pyalte (1969) have pointed out that the determination of an optimal or hierarchical sequence of subtasks from simplest to most complex is not easi ly achieved.