 The approximation that constitutes classical irreversible thermodynamics is built on this metaphoric thinking.As indicated by the " " marks of Onsager (1931), such a metaphorical but not categorically mechanical force, the thermal "force", formula_1, 'drives' the conduction of heat.For this so-called "thermodynamic force", we can write
Actually this thermal "thermodynamic force" is a manifestation of the degree of inexact specification of the microscopic initial conditions for the system, expressed in the thermodynamic variable known as temperature, formula_3.