We present two opposing views of which thermodynamic function of state should be used to predict phase changes in stressed matter in general. We have considered if each view might be false on the basis of whether each function of state is consistent with the Gibbs free energy in the isotropic stress limit. We have shown that one function of state is consistent with the Gibbs free energy in the isotropic stress limit, whereas the other function of state appears to be inconsistent with the Gibbs free energy in the isotropic stress limit. We submit that those who support the other function of state would strengthen their case if they could show that the other function of state is consistent with the Gibbs free energy in the isotropic stress limit, unless some robust argument can be advanced which undermines our methodology. (C) 2007 Elsevier B.V. All rights reserved.