 Mill gives the example of the science of the tides. Physicists determined the law of gravitation by studying planetary motion, in which gravity is the only significant causal factor. Then physicists develop the theory of tides deductively from that law and information concerning the positions and motions of the moon and sun. The implications of the theory will be inexact and sometimes badly mistaken, because many subsidiary causal factors influence tides. Testing theories of tides can uncover mistakes in the deductions physicists made, and it may uncover evidence concerning the role of the subsidiary factors. But because of the causal complexity, such testing does little to confirm or disconfirm the law of gravitation, which has already been established. Although Mill does not often use the language of “ceteris paribus”, his view that the principles or “laws” of economics hold in the absence of “interferences” or “disturbing causes” provides an account of how the principles of economics can be true ceteris paribus (Hausman 1992, ch. 8, 12).