  Philosophers of science have been intrigued by ideals of reductionism and the grand scheme that all science will one day be “reduced” to a universal science of fundamental physics (see the entry on  inter-theory relations in physics)  for philosophical and scientific concepts of reductionism in the context of physical science). Philosophical reductionists believe that scientific knowledge progresses when higher-level sciences (e.g., chemistry) are reduced to lower-level sciences (e.g., physics). The so-called received view of scientific knowledge, codified in Nagel (1961) and Hempel (1966), promoted reductionism as a central ideal for science, and confidently asserted that much progress had been made in the reduction of chemistry to physics. Nagel constructed a formal model of reduction and applied it to illuminate how the science of thermodynamics, which was couched in terms of higher-level concepts such as pressure and temperature, was allegedly reduced to statistical mechanics, couched in terms of the lower-level concepts of Newtonian dynamics such as force and mean kinetic energy. In 1969, Schaffner claimed that the same kind of advance was now taking place in genetics, and that the science of classical genetics was being reduced to an emerging science of “molecular genetics.” Schaffner's claim, however, was quickly challenged by Hull. Other philosophers of biology developed Hull's anti-reductionist arguments and a near consensus developed that classical genetics was not and would not be reduced to molecular genetics. Although the philosophical case for anti-reductionism has been challenged, many philosophers still assume that the anti-reductionist account of genetics provides an exemplar for anti-reductionist analyses of other sciences.