Descriptive Strength and the Adequacy of Implementation Claims

Abstract This chapter introduces three classes of computational descriptions of physical systems (CDPSs) of increasing strength, defined by which of four strength criteria they satisfy. Two of these criteria—the criteria S (for state) and P (for process) introduced in Chapter 3—are defining criteria for any CDPS. The two remaining criteria—criteria PCE (for physical-computational equivalence) and U (for usability) introduced in this chapter—go further. CDPSs are classified as weak if they satisfy S and P but not PCE or U, robust if they satisfy S, P, and PCE but not U, and strong if they satisfy all four criteria. The chapter then outlines a framework for evaluating claims about implementation based on this strength classification, which helps to reveal what one must accept about the nature of physical implementation if one is to accept that claim as adequate.