Conceptual design synthesis, which focuses on generating solution alternatives, has a significant impact on the cost and quality of the final product. The development of radically new and significantly better solutions requires the generation and exploration of a large solution space. This work deals with the conceptual design synthesis of multi-state mechanical devices (MSMD). A scheme for representing a MSMD design task is described. Empirical studies have been carried out to develop a common understanding of the MSMD design synthesis process and use this knowledge for developing a prescriptive model. In order to support the effective and efficient use of the proposed prescriptive model, a web-based computational tool is developed.