In the philosophy of science, under the correspondence principle, a limiting case theory is an earlier theory which becomes incorporated into a later, usually broader theory; that is to say, the earlier theory proves to be a special or limited case of the later theory. Technically, a theory is said to be a limiting case of another, later theory when and if the later theory subsumes the theoretical relations and apparent referents of the earlier one. For example, physicists agree that classical mechanics constitutes a low-energy limiting case of relativity theory.