 (c) Hull (1976), Wimsatt (1976a, 1976b), and Sahotra Sarkar (1992, 1998) have objected that Schaffner focuses too much on formal considerations about reduction, rather than substantive issues. His account construes reduction as a logical relation that is “in principle” possible even though it is not occurring in practice. If reduction in this sense is not occurring in biology, then there are significant questions about whether it best fits biological knowledge and practice. Nagel claimed that premature attempts at reduction could retard scientific progress, thus implicitly decoupling methodological demands from epistemological ones (Nagel 1961, 362–3). Schaffner (1974, 1993) acknowledges that reductionism in his sense has been peripheral to the practice of molecular biology, but maintains that his formal model of reduction captures the reduction relation between theories. Wimsatt (1979) suggests that Nagel’s and Schaffner’s focus on in-principle considerations and the context of justification, to the exclusion of in-practice considerations and the context of discovery, leads to misunderstandings about the nature of reductionism debates, including historical and current controversy among scientists (see  Section 2).  Reduction may obtain between classical and molecular genetics, but not in the sense of Nagel’s or Schaffner’s logical empiricist approach (Hull 1974).