  Finally, the second and third segments together not only point out that Keplerian motion is only an approximation to the true motions, but they call attention to the potential pitfalls in using the orbits published by Kepler and others as evidence for claims about the planetary system. For example, if the true motions are so complicated, then it is not surprising that all the different calculational approaches were achieving comparable accuracy, for all of them at best hold only approximately. Equally, the success in calculating the orbits could not serve as a basis to argue against Cartesian vortices, for the irregularities entailed by them could not simply be dismissed. The spectre raised was the very one Newton had objected to during the controversy over his earlier light and color papers: too many hypotheses could be made to fit the same  data.[10] Worse, the multiplicity of tenable hypotheses was a spectre haunting mathematical astronomy as a discipline from the end of the sixteenth century  forward.[11] So, the conclusion that calculated orbits can at most be mere approximations would have been seen as raising the possibility that truth and exactness were beyond the reach of mathematical astronomy. The main reason why the Principia includes so much beyond the “De Motu” tract is Newton's endeavor to reach conclusions that had claim to being exact and true in spite of the inordinate complexities of the actual motions.