We agree that treating rules and similarity as dichotomous opposites is unproductive. However, describing all categorization operations as a continuum of varied similarity process obscures a multidimensional contrast. We describe two processes, instantiated rules and abstract analogy, both of which have aspects of rules and similarity, and question whether they can be compared informatively as points on a continuum.

Medical education provides many examples of the development of functional features, but as a response to deliberate instruction. These features require so much specificity and context sensitivity that they seem likely to require the development of new categories of appearances rather than just reweighting old features. A suggested implication is that feature development may help to explain the problematic noticing of features in diagnosis.