 Like the semantic and syntactic accounts, the mechanistic account aims to avoid pancomputationalism. First, physical systems that are not functional mechanisms are ruled out. Functional mechanisms are complex systems of components that are organized to perform functions. Any system whose components are not organized to perform functions is not a computing system because it is not a functional mechanism. Second, mechanisms that lack the function of manipulating medium-independent vehicles are ruled out. Finally, medium-independent vehicle manipulators whose manipulations fail to accord with appropriate rules are ruled out. The second and third constraints appeal to special functional properties—manipulating medium-independent vehicles, doing so in accordance with rules defined over the vehicles—that are possessed only by relatively few physical systems. According to the mechanistic account, those few systems are the genuine computing systems.