Performance or capacity, the model still requires definitions and boundaries it doesn't have

Siegel is correct that, in its current form, the specific constructs underlying the Demands and Capacities Model cannot be adequately defined. However, substituting observable behavior (performance) for presumed underlying weaknesses in the speech production systems of those who stutter (capacity) does not appear to solve the problem of circularity identified. Rather, demands have not been adequately defined, either. There is much to agree with in Siegel's note. However, it is not clear to me that the Demands and Capacities Moder is salvaged by substituting the term "Performance" for "Capacity." Rather, the problem with the Model is one of defining terms precisely enough so that the Model is not circular (as Ingham & Cordes (1997) have noted), or the logical inverse of Procruste's bed, as I have stated elsewhere (Bernstein Ratner, 1997), a model that fits all interpretations simply because it stretches to fit all possibilities. (C) 2000 Elsevier Science Inc.