The thermodynamic aspects of the methods commonly used in thermogravimetric analysis, that is, isothermal and dynamic, are presented. Models for isoconversional variants of dynamic methods are accepted. For the thermal dissociation of the solid phase, the free enthalpy of the system, called the Gibbs free energy state, and the stoichiometric principles according to de Donder's extent of reaction, were proposed as the starting point, binding the dissociative pressure in the gas phase with the rate of solid phase conversion. It was found that the isothermal methods and, surprisingly, the dynamic methods, occur in one system group, although with different energetic activity, whereas isoconversional variants of dynamic methods represent opposite effects in this range. Off-distance, which is formally defined as D = Delta Delta G, was proposed for the quantification of each analyzed case. According to the presented considerations, the isothermal and dynamic methods are dominated by enthalpy, whereas isoconversional methods are dominated by entropy.