  The historical context in which Newton wrote the Principia involved a set of issues that readers of the first edition saw it as addressing: Was Kepler's approach to calculating the orbits, or some other, to be preferred? Was there some empirical basis for resolving the issue of the Copernican versus the Tychonic system? Were the true motions complicated and irregular versus the calculated motions? Can mathematical astronomy be an exact science? No reader of the Principia at the time had the benefit of seeing how Newton had these questions tied together in the “Copernican Scholium” because it did not appear in print until two hundred years  later.[12] Nothing, however, brings out more clearly the extent to which the expanded scope of the Principia stemmed from Newton's preoccupation with the problem of reaching conclusions that had claim to being exact from evidence that, by his reckoning, held at best to high approximation. This is why the “Copernican scholium” provides the most illuminating context for reading the Principia. Equally, its being unknown for so long helps to explain why the Principia has generally been read so simplistically.