A classificatory theory of similarity

Summary This paper outlines a classificatory theory of cognitive similarity and compares it to feature approaches. The theory assumes that similarity is a function of the number of classes contained in the universe referred to in the judgments and the number of elements contained in the class defined by the two comparison stimuli. The theory is tested in a number of studies in which verbal stimuli are used. Most of the experiments concern context effects predicted by the theory. An empirical comparison is made between the classificatory theory and a feature theory. It is argued that the classificatory theory accounts for some of the data more easily than a feature approach does. Some implications for the use of similarity data in multidimensional scaling are also discussed.