 Many reductionist philosophers subsequently elaborated on Lewis’s point with the help of scientific examples. Patricia Churchland (1986: Chapter 7), Clifford Hooker (1981), Berent Enç (1983), and other philosophers of science have described historical intertheoretic reductions where a given reduced concept is multiply realized at the reducing level. A common example is the concept of temperature from classical equilibrium thermodynamics. Temperature in a gas is identical to mean molecular kinetic energy. Temperature in a solid, however, is identical to mean maximal molecular kinetic energy, since the molecules of a solid are bound in lattice structures and hence restricted to a range of vibratory motions. Temperature in a plasma is something else entirely, since the molecular constituents of a plasma have been ripped apart. Even a vacuum can have a (“blackbody”) temperature, though it contains no molecular constituents. “Temperature” of classical thermodynamics is thus multiply realized microphysically in a variety of distinct physical states. Yet this is a “textbook” intertheoretic reduction in the history of science. It is just that the reduction, and the subsequent ontological identifications across theories, are specific to the domain of physical state.