Kepler's Philosophy and the New Astronomy

UNTIL NOW MY FOCUS has been the positive influence of Kepler's archetypal cosmology on his epistemology and methodology. Although his cosmology, like his physics, is no longer part of the scientific canon, it retains significance in virtue of its contribution to Kepler's lasting achievements. To the modern mind, the archetypes are valuable for the roles they played in his astronomical work. But it was his contemporaries that Kepler needed to persuade, not us, and it was his physical astronomy that he needed to defend, not his cosmology. Kepler would have found useful a rhetorical platform from which to justify his radical discoveries, and he had the skill to construct one. Both Jardine (1984, 75) and Stephenson (1987, 3) note that Kepler took care to write the Apologia and Astronomia in a manner designed to win over opposition. I argue that Kepler's archetypal cosmology was a crucial part of this platform, allowing him to avoid straying too far from the Aristotelianism dominant during his time. Despite Kepler's avowedly Platonic and Pythagorean sympathies, his physical astronomy fit well with Aristotle's directives in the Posterior Analytics. Perhaps paradoxically, the archetypal cosmology of the Mysterium enabled the merging of Platonic and Aristotelian intuitions in Kepler's new astronomy.

The corpus Aristotelicum, though no longer the authority it had been in late medieval times, was still the foundation of university curricula in the sixteenth century. This arrangement was true of Tübingen, Kepler's alma mater, although some of Kepler's teachers, notably Andreas Planer and Michael Maestlin, were well acquainted with Neoplatonism and Copernicanism.¹ Schmitt (1975, 489) suggests that despite various challenges to Aristotelian natural philosophy, its overthrow was inhibited by the lack of alternative approaches equally extensive and systematic. As a result, Aristotelianism was taken as the alpha, though by no means the omega, of approaches to natural philosophy²

As noted earlier, in Kepler's time there was cause for concern about the status of astronomy. There were competing astronomical hypotheses,

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