 Nagel’s model was revised and applied in a specifically biological context—the reduction of classical genetics to biochemistry—by Kenneth Schaffner (1967, 1969, 1976; see Schaffner 1993 for his mature account). Schaffner’s “General Reduction Model” addresses a key drawback of Nagel’s account, first noted by Feyerabend: even though the theory to be reduced may be approximately true, it might contain empirically false statements, especially if it is a historical precursor of the more mature reducing theory (e.g., the inheritance “laws” of classical genetics have exceptions). If the theory to be reduced (TB) contains false statements then it  cannot possibly be deduced from TA. For this reason, Schaffner considers instead TB*, which is a corrected version of the theory to be reduced in that TB* makes more adequate predictions than TB. On this model, reduction occurs if TA and TB* can be related by reduction functions (bridge principles) and TB* follows logically from TA enriched by the reduction functions. (While Nagel focused on the laws of TB being deducible from TA, Schaffner requires that all statements of TB/TB* be deducible from TA.) Schaffner’s central tenet about reduction in biology is that the success of  molecular biology  shows that classical genetics and traditional fields of experimental biology are in the process of being reduced to biochemistry. Although this reduction has not been completed yet, a logical derivation of traditional experimental biology from a (completed) theory of biochemistry is in principle possible and will be achieved eventually. Schaffner’s account has an ontological aspect in that he interprets the reduction functions as synthetic statements expressing identities between the entities and processes of the two domains related (in line with Sklar 1967 and Causey 1972a, 1972b), though he does not argue that these identities are metaphysical necessities. The Nagel-Schaffner approach to theory reduction assumes a syntactic account of  theory structure  such that they are axiomatized systems formalizable in first order predicate calculus. A variety of other models of theory reduction exist, some of which use a semantic (i.e., theories as families of  models)  rather than a syntactic account of scientific theories (see Balzer and Dawe 1986a,b, Hooker 1981, Suppes 1957, Woodger 1952).