Kepler’s Geometrical Music Theory: Philosophical Motivations and Significance

In Book III of his Harmonices Mundi Libri V, Kepler delivers his theory of musical harmony. The account that he provides is striking in that it is exceptionally detailed, complex, and highly original, making a significant break in its approach when compared to other theories offered at the time. However, rather than sparking a new trend, Kepler’s theory remained an outlier. All these considerations compel us to inquire into why Kepler was drawn to his particular account of musical harmony. In this paper, I will show that several philosophical considerations converged to lend support for his account. These considerations are of two types: those that stem from Kepler’s broader theoretical framework and those that can be seen as free-standing. Attending to Kepler’s theory of harmony in this way is important for a couple of reasons. First, it brings out its place within his broader philosophical program and, second, it provides a particularly interesting case of a philosopher in this period weighing considerations of internal consistency, empirical adequacy, and target precision in the formation of a highly original and complex account. Thus, it is important more broadly for understanding philosophical methodology and theory formation in this period.