The mechanisms of phase separation in colloidal systems as laid out in the volume-term theories, the Sogami-Ise model, and the Langmuir unipolar coacervation model are shown to have a common bond through standard thermodynamic relationships between the Gibbs free energy, the Helmholtz free energy, and the chemical potential. This leads to the interesting observation that the validity of the individual approaches is intrinsically tied to the validity of the generalized volume-term approach.