 Another, influential set of challenges to theory reduction in genetics is posed by Philip Kitcher (1984). The main problem, and indeed one that is fundamental to any account of theory reduction that identifies theories with sets of laws, is that there are no laws in classical genetics. Even seemingly straightforward examples such as what came to be called “Mendel’s laws”, as Kitcher shows, are neither laws, nor do they play an important explanatory role in classical genetics. Kitcher further argues that the basic predicates of classical genetics, such as “x is a gene” cannot be unequivocally connected to the vocabulary of molecular genetics through bridge principles, as it would be required for successful theory reduction. Finally, even if these two issues were solved, an account based on the principles of molecular genetics would not explain the phenomena of classical genetics any better than the cytological explanations already in place. Others argue against this disunified picture of Mendelian and molecular genetics that the two fields depend on each other in their practices. This interdependence, however, also precludes an eliminative reduction (i.e., replacement) (Vance 1996).