Could There be Method Behind Kepler's Cosmic Music?

While Kepler is regarded as a major figure in standard historical accounts of the scientific revolution of early modern Europe, he is typically seen as having one foot in the new scientific culture and one in the old. In some of his work Kepler appears, along with Galileo, to be on a trajectory towards Newton’s celestial mechanics. Besides his advocacy of Copernicus’s heliocentrism, he appeals to physical causes in his explanations of the movements of celestial bodies. But other work expresses a neo-Platonic “metaphysics” or “mysticism”, as most obvious in his self-alignment with the ancient tradition of the “music of the spheres”. Here I problematize this distinction. Kepler’s purported neo-Platonic “metaphysics”, I argue, had been tied to Platonic and neo-Platonic features of the methodology of a tradition of mathematical astronomy that would remain largely untouched by his shift to heliocentrism and that would be essential to his actual scientific practice. Importantly, certain inherited geometric practices—one’s later formalized as “projective geometry”—would carry those “harmonic” structures expressed in the thesis of the music of the spheres.