Some remarks and clarifications concerning the restrictions placed on thermodynamic processes

Various disparate restrictions are assumed with regard to bodies undergoing thermodynamic processes, in addition to the second law, to cull the class of constitutive relations for describing their response. In this paper we critically evaluate some of these additional restrictions. After a brief discussion of the various forms of the second law due to the pioneers in the field we turn our attention to an assessment of additional stringent restrictions due to Onsager, Prigogine, Ziegler, and Edelen. With the use of specific examples we show the pitfalls and inadequacies of these additional restrictions. The importance of identifying the “cause” (which we refer to as the “determinant” which is incorrectly referred to as “flux”) and its “effect” (which we refer to as the “resultant” which is incorrectly referred to as “affinity”) and not merely splitting the “determinant” on the basis of mathematical ease rather than understanding the underlying physics, is emphasized by considering specific examples.