The incorporation of precedents into a present design situation by adaptation, restructuring and reformulation depends upon processes of typification and generalization. The function of prototypes as a characteristic form of generalized and structured knowledge in design is described. A precedent-based design model employing memory-based reasoning is proposed. It is argued that typological concepts can serve as a matching level between situation types and solution types. In such an approach both the organization of structured knowledge and the mechanisms of matching to prior knowledge such as cross-indexing and analogy appear to be of seminal importance. A memory-based reasoning process in routine, innovative and creative design is postulated. This is based on concepts of dynamic and episodic memory. Relevant work in the fields of memory organization, machine learning and analogical reasoning is considered with respect to its significance to the field of knowledge-based design