Formal causes and immediate causes: the analogy of the musical instrument in late-seventeenth-century natural philosophy

Abstract

The concept of 'harmony' had been important in constructing models of the cosmos since antiquity. During the seventeenth century we see a shift, however, from harmony as formal cause to the use of musical metaphors and models to provide mechanical explanations, that is immediate causes.

1. Harmony as formal cause: Kepler's Harmonices mundi is an example of this, from the early seventeenth century, in which it is axiomatic that the same ratios which govern the solar system also govern instrumental music. Marin Mersenne extended the scope of 'harmony' to encompass many new fields of knowledge, and Robert Fludd drew attention to the idea of 'universal harmony' with his diagrams of the correlation between cosmic and human harmonies. One of the few examples from the later seventeenth century is Newton's division of the spectrum according to the proportions of a stringed musical instrument.

2. Musical analogy for immediate cause: Robert Hooke, for example, regularly appealed to the analogy of a musical instrument to explain the small-scale properties of matter, the force of gravitation and even the structure of the cosmos. Robert Boyle extended its use in different ways, for instance to the attraction of angels by the philosopher's stone. In some texts Newton engaged with the idea that a musical analogy of mechanical vibration could explain the function of human vision. Similarly the anatomist Thomas Willis used analogies of musical instruments and vibrating strings for the functions of the human brain, an idea which Hooke also took up. A possible link with earlier sources is provided by the astronomer Jeremiah Horrocks, who suggested re-founding Kepler's harmony of the spheres on a mechanical analogy of vibration and resonance.

I will reflect on the significance of this change, and the role of musical models in it. It relates to the well-known epistemic shift of this period: but a desire to retain some link with the older harmonic explanations is also revealed. Perhaps surprisingly, these new musical analogies did not lead to the widespread use of musical skills, judgement, or instruments in the practice of natural philosophy.