 In ascribing geometrical knowledge of the five regular solids to Pythagoras, Kepler is following an erroneous Neopythagorean tradition, although the dodecahedron may have served as an early Pythagorean symbol (see on Hippasus in section 3.4 above and Burkert 1972, 70–71, 404, 460). Thus, this aspect of Kepler’s work is more Platonic than Pythagorean. The five solids were conceived of as circumscribing and inscribed in the spheres of the orbits of the planets, so that the five solids corresponded to the six planets known to Kepler (Saturn, Jupiter, Mars, Earth, Venus, Mercury). There were six planets, because there were precisely five regular bodies to be used in constructing the universe, corresponding to the five intervals between the planets. This view was overthrown by the later discovery of Uranus as a seventh planet. Kepler’s cosmology was, however, far from a purely a priori exercise. Whereas his contemporary, Robert Fludd, developed a cosmology structured by musical numbers, which could in no way be confirmed by observation, Kepler strove to make his system consistent with precise observations. Kahn suggests that we here see again the split “between a rational and an obscurantist version of Pythagorean thought,” which is similar to the ancient split in the school between mathematici and acusmatici (2001, 163).