Modeling modeling.

Models are tools; they need to fit both the hand and the task. Presence or absence of a feature such as a pacemaker or a cascade is not in itself good. Or bad. Criteria for model evaluation involve benefit-cost ratios, with the numerator a function of the range of phenomena explained, goodness of fit, consistency with other nearby models, and intangibles such as beauty. The denominator is a function of complexity, the number of phenomena that must be ignored, and the effort necessary to incorporate the model into one's parlance. Neither part of the ratio can yet be evaluated for MTS, whose authors provide some cogent challenges to SET.