The Problem of Class Breakdown in Sidman's (1994, 2000) Theory about the Origin of Stimulus Equivalence.

Sidman (1994, 2000) hypothesized that equivalence relations are a direct outcome of reinforcement contingencies. This theory is problematic because contingencies do not always result in equivalence. Sidman proposed that equivalence relations may conflict with analytic units, the other outcome of contingencies (e.g., in conditional discriminations with common responses/reinforcers). This conflict may result in a generalized class breakdown and a failure to pass equivalence tests. This is more likely in nonhumans, very young humans, etc. The conflict can also result in a selective class breakdown and success in equivalence tests. This occurs after experience shows the organism the necessity and utility of this process. The nature of that experience and the class breakdown processes were not described by Sidman. I explored the implications of the following hypotheses for Sidman's theory. First, conditional discriminations with a common response/reinforcer result in a generalized class breakdown when participants fail to discriminate emergent relations incompatible with contingencies from those compatible. Second, learning to discriminate between the two requires a history of multiple exemplar training (MET). This implies that equivalence class breakdown is a common response to exemplars that have nothing in common except their relations. This, however, contradicts Sidman's views about the impossibility of such process in the absence of a complex verbal repertoire. If that type of learning from MET is possible, then the possibility that MET results in the selective formation of equivalence classes must be admitted, and the utility of hypothesizing that equivalence is a direct outcome of reinforcement contingencies can be questioned.