Basic principles of concept development dictate that a complex or abstract idea must be grasped as a result of many experiences with more concrete objects containing exemplars of the idea. The implications for the teacher are that he must select a wide variety of materials and activities in which an abstract idea is suggested quite prominently, yet is experienced in a reasonably natural setting. Thus, in the course of concept development, exemplary materials are modulated from simple to complex, obvious to subtle and concrete to abstract, as the teacher assists the student in discovering their common elements. Generally, music educators have accepted and applied these wellestablished ideas and methods; however, there is less unanimity of thought and practice among them with regard to details such as the relative merits and effects of using negative as well as positive exemplars in concept development. In a survey of musical style periods, for example, where objectives include the development of broad stylistic concepts, music educators have not been able to agree whether exclusive emphasis should be given to the similarities of the diSerent musical compositions within each of the musical eras studied or whether frequent reference also should be made to music that is in contrast to the music of the period under surveillance. Music educators do not agree on whether the student should be presented only with as many examples as possible of how the music of any given style should sound, or whether they also should be presented with clear examples of how it does not sound. Only a limited amount of research literature-that in the general area of educational psychology-is available to shed light on such