This paper explores the implications of the fact that most attitudes are embedded in a hierarchy of beliefs about concepts that are either more abstract or less abstract than the attitude being considered. Attempts to change attitudes can be made by sending messages at any or all levels of abstraction. An information processing model is proposed: (a) to provide a description of the changes in the multi-level system over time when messages are sent at various levels, and (b) to explain the generalization of attitude change, delayed attitude change effects, and the fact that attitude change may or may not decay over time. Individual differences in the external parameter are shown to be related to persuasibility while differences in the internal parameter are related to dogmatism. Thus, persuasibility and dogmatism are sharply differentiated in this model.