The Compound Energy Formalism was not developed by using standard statistical mechanical procedures. If it had been, the model would have been based on cluster solution members instead of on compound end members. In its present form, using the Bragg – Williams approximation, the distinction between these two types of entity has no impact on the model's application, with one notable exception – the case of vacancy properties in intermediate phases. The distinction between the two viewpoints becomes more significant, however, for the future development of the model. It is not clear how short range order or the effects of atomic size mismatch can be explicitly taken into account in its compound end member form. Both of these features are readily absorbed into the model, however, when cluster solution members are considered to be the important entities.