 One way to be selective is to draw a distinction between working posits of a theory (viz., those theoretical posits that occur substantially in the explanatory schemata of the theory) and presuppositional posits (putative entities that apparently have to exist if the instances of the explanatory schemata of the theory are to be true) (cf. Kitcher 1993: 149). Another way is to draw a distinction between the theoretical claims that essentially or ineliminably contribute to the generation of successes of a theory and those claims that are ‘idle’ components that have had no contribution to the theory’s success (cf. Psillos 1994, 1996). The underlying thought is that the empirical successes of a theory do not indiscriminably support all theoretical claims of the theory, but rather the empirical support is differentially distributed among the various claims of the theory according to the contribution they make to the generation of the successes. Generally, Kitcher (1993) and Psillos (1996, 1999) have argued that there are ways to distinguish between the ‘good’ and the ‘bad’ parts of past abandoned theories and to show that the ‘good’ parts—those that enjoyed evidential support, were not idle components and the like—were retained in subsequent theories.