The target article extends molar behaviorism in two positive ways: beyond average aggregates and beyond restricted laws of Although a molar framework based on purely overt events shows promise for advancing behavior theory, Rachlin's specific form of teleological behaviorism is in need of clarification.

Hull et al.'s analysis of operant behavior in terms of interaction and replication does not seem consistent with a genuine selection model. The putative replicators do not replicate, and the overall process is more reminiscent of directed mutation than of natural selection. General analogies between natural selection and operant reinforcement are too superficial to be of much scientific use.

The research Nevin & Grace report is impressive in its integrative power, but it also shows the current limits of operant theory: There is tremendous concentration on understanding how existing behavioral relations are modulated in rate or time allocation, but little on dealing with the origin of the behavioral relations themselves. Specifying what should count as a behavioral unit will require source principles sensitive to the composition of the units being related.