The equation of state developed by Segletes is compared with prior theories. By modifying the functional relationship for the &psgr; variable and eliminating higher order terms, each of three historical theories for the Gru¨neisen function can be made to fall directly out of the model—namely, the theories of Slater, Dugdale and MacDonald, and the free-volume theory. One concludes that Segletes’ model captures the essence of all of the older theories, each of which being nominally applicable under an appropriate circumstance. The current model differs, however, from these historical models, if the higher order terms are retained. ©1998 American Institute of Physics.