Distances between stimuli and, derivatively, compactness of stimulus subsets are pervasive determiners of discrimination and classification performance. Contrary to Crassini (1986), these factors are sufficient to account for the major patterns in the chronometric data of Podgorny and Shepard (1978, 1983). Other factors, such as the dichotomous one distinguishing what Crassini terms unitary and nonunitary subsets, may exert some additional influence. But a convincing demonstration would require formulation of a quantitative model capable of being pitted against the distance-based model of Podgorny and Shepard within the context of their entire body of data.