Concept identification problems with a single relevant dimension may be solved in two stages: the selection of the relevant dimension and the learning of appropriate responses to the values of the dimension. Such a theory was investigated by manipulating the number of response categories (four, six, or eight) in a 3 by 3 design involving 90 human subjects. Errors were found to increase with increases in response categories during all stages of problem solution, with a linear increase for paired associate and complete learning conditions. The results were interpreted as supporting a theory incorporating overlapping dimension selection and paired associate processes.