Simon et al. (2020) argue that the concept of response strength is unnecessary and potentially harmful in that it misdirects behavior analysts away from more fruitful molar analyses. I defend the term as a useful summary of the effects of reinforcement and point particularly to its utility as an interpretive tool in making sense of complex human behavior under multiple control. Physiological data suggest that the concept is not an explanatory fiction, but strength cannot be simply equated with neural conductivity; interaction with competing behaviors must be considered as well. Decisions about appropriate scales of analysis require a clarification of terms. I suggest defining behavior solely in terms of its sensitivity to behavioral principles, irrespective of locus, magnitude, or observability. Furthermore, I suggest that the term response class be restricted to units that vary together in probability in part because of overlapping topography. In contrast, functional classes are united by common consequences; they vary together with respect to motivational variables but need not share formal properties and need not covary with acquisition and extinction contingencies.
Keywords: Definition of behavior; Functional classes; Inhibition; Response classes; Response competition; Response strength.
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