With an emphasis on procedural fundamentals, the original behavior-analytic equivalence experiments and the equivalence paradigm are described briefly. A few of the subsequent developments and implications are noted, with special reference to the possible significance of the findings with respect to language and cognition. (Contains 9 figures.)

To provide the first systematic test of whether young children will spontaneously perceive and imitate hierarchical structure in complex actions, a task was devised in which a set of 16 elements can be modelled through either of two different, hierarchically organized strategies. Three-year-old children showed a strong and significant tendency to…