 Perhaps the most common approach to weak emergence is one appealing to one or other account of “realization”. (Recall the point made in  section 2.1.2  that realization falls under the more general concept of grounding that is deployed more frequently in some other contexts.) The first accounts of realization were in functionalist terms, according to which a realized feature is characterized by a distinctive causal or functional role, which role is implemented, on any given occasion, by some or other lower-level physical feature. Hence, Putnam (1967) suggests that, just as a software program might be implemented on multiple hardware platforms, so mental states might be associated with causal-functional roles which are played by multiple neurological, and ultimately fundamental physical, states. Such an approach accommodates the ontological autonomy of weak emergents to the extent that a functionally associated type is not identified with any one of its realizer types. It would also appear to provide a basis for blocking concerns about causal overdetermination by analogy again to software programs, whose powers are inherited from their lower-level realizers. Given such an inheritance thesis for higher-level powers, even if there is a sense in which both realized and realizing features can cause a given effect, only one power is exercised, not two—in which case, it is maintained, the overdetermination is benign. (This functionalist perspective on special science entities and features was influentially developed by Fodor 1974.)