  Interpreting Newton's deduction of universal gravity as an exercise in approximative reasoning answers a further complaint of Duhem's: insofar as the area rule holds only to high approximation, so too do any number of alternatives to it, such as Boulliau's geometric construction, and hence Newton's “deduction” begs the question of why the area rule is to be preferred to these  alternatives.[46] This question, however, is irrelevant so long as the conclusion remains in the weak form, the law of gravity holds quam proxime for the planets and their satellites over the time period for which observations have shown the phenomena to hold quam proxime. The phenomena really are sufficient to reach the conclusion in this weak form. So, the complaint has bite only when the law of gravity is taken to be exact. But there, however, Newton does provide a response to it when he concludes in Propositions 13 and 14 that the planets would describe areas exactly proportional to the times in stationary orbits if “the Sun were at rest and the remaining planets did not act upon one  another.”[47]  The reason, then, why the phenomena from which Newton proceeded in the deduction have claim to being preferred to alternatives to them is that the theory deduced from them, when taken to hold exactly, identifies circumstances under which the phenomena would hold exactly, as well. That this be the case amounts to a requirement on the deduction from phenomena: the leap to taking the law of gravity as exact is justified only if it yields circumstances in which the phenomena from which it was inferred would hold  exactly.[48]