For this post, I turn to an unlikely protagonist, self-proclaimed bad musician Denis Diderot, polymath of the French Enlightenment.
Dissonance takes center stage in Diderot’s Neveu de Rameau, or Rameau’s Nephew, written in 1761, revised substantially in 1773 and 1774, and published posthumously in 1805. Rameau’s Nephew is a dialogue between Diderot and the fictional nephew of Jean-Phillippe Rameau, composer and theorist of the eighteenth century. We learn that the nephew is a rough outcast: he was recently dismissed from his court position on account of his insubordination, a damaging willingness to speak out of turn—to dissonate against the insipid consonance of courtly politesse. Significantly, Rameau’s nephew relishes his dissonance; he insists upon it during moments of musical pantomime. As Diderot scholar Andrew Clark has shown, through the nephew’s body, we are meant to experience dissonance as an integral part of musical and narrative aesthetics.
The depiction of dissonance in Rameau’s Nephew highlights Diderot’s philosophical materialism, informed by his engagement with music over the course of his life. Diderot’s musical materialism was a theory unique among his contemporaries. He imagined the universe to be filled with vibrating, inherently active and reactive matter. Musicians like Rameau’s nephew possessed “readily harmonic” bodies: their natural states, shaped by knowledge and practice, afforded them access to a dynamic and sensual world of bon goût.
Interestingly, Diderot’s musical materialism crops up in a contemporaneous document of music theory, Antoine Bemetzrieder’s Leçons de clavecin, or “Keyboard Lessons,” which Diderot edited and saw through to publication in 1771, only two years before he revised Rameau’s Nephew. Like Rameau’s Nephew, the Lessons is a dialogue between a young female keyboardist, her teacher, Bemetzrieder, and Diderot, cast in the role of “Philosophe.” Musicologist Jean Gribenski has illustrated how Bemetzrieder’s unassuming keyboard tutor overlaps remarkably with Diderot’s own philosophical outlook. While provenance and influence are difficult to ascertain, it is likely that Diderot edited the Lessons in order to accentuate these concordances. The most intriguing aspect of the treatise is Bemetzrieder’s theory of the grande dissonance, or “great dissonance,” and the theorist’s principle for the resolution of dissonance, the appel, or “call.” Bemetzrieder formulates his theory as an extension of arguably the best-known music-theoretical principles of his day, the concepts of the fundamental bass and the corps sonore, developed in the first half of the eighteenth century by Jean-Phillippe Rameau.
In his theory of the fundamental bass, Rameau asserted that, within a harmonic progression, every non-tonic harmony contained within it a dissonant seventh, whether or not the seventh was articulated or audible. Rameau’s theories were addled by problems related to musical subjectivity. Even if no dissonance manifested in the non-tonic chords between iterations of the corps sonore, Rameau insisted that the performer or listener imagined a chordal seventh where one ought to have been. Therefore, all non-tonic sonorities were unstable even if there was nothing physically dissonant about them.
Bemetzrieder imagines the “great dissonance”—a chord composed of the pitches B, D, F, and A—as a natural companion to the corps sonore. As the character of the Philosophe, Diderot amplifies Bemetzrieder’s theory thus:
In this great dissonance of the leading tone [sensible], followed by the corps sonore with all its overtones, my ear is offered first all the dissonants [dissonnans] of the scale [game], pure and unmixed, and then the corps sonore and its retinue, with each in their natural position, the scale divided sharply into two portions: on one side that which nature has produced; on the other that which art has conjured to enhance nature and make [nature] desirable. 
Given that Diderot edited the Lessons and likely exerted some influence over what his character might say, I underscore here how the Philosophe theorizes musical dissonance. With his insistence on music’s audible and material dynamism, motivated on the one hand by the stability of consonance and on the other by dissonance’s natural expressiveness, Diderot fortifies Bemetzrieder’s pedagogy with his materialist outlook. For Bemetzrieder and Diderot, the scale is an emblem for the vibrant physical interactions among natural phenomena. On their account, every sonority contains the materials for the production of consonance and dissonance. Dissonance does not, as Rameau indicated a generation prior, inhere in sound as an ideational concept; it becomes a productive material state rather than a foreign entity to be purged.
Together, Rameau’s Nephew and the Lessons shed light on a philosophical take on dissonance that is more discursive than empirical. For Diderot, good musical taste was a constant dialogue between consonance and dissonance. And framed as exchanges between people, either real or imagined, Diderot’s texts insist on discourse amid a flurry of eighteenth-century quarrels and polemics.
 Andrew Herrick Clark, Diderot’s Part (Burlington: Ashgate, 2008), 144.
 On the notion of “readily harmonic” bodies, see Matthew Riley, “Straying From Nature: The Labyrinthine Harmonic Theory of Diderot and Bemetzrieder’s Leçons de clavecin (1771),” The Journal of Musicology 19, no. 1 (2002), 23.
 Jean Gribenski, “À Propos des Leçons de clavecin (1771): Diderot et Bemetzrieder,” Revue de musicologie 66, no. 2 (1980), 126.
 For detailed commentary on Rameau’s fundamental bass theory, see Christensen, Rameau and Musical Thought in the Enlightenment (Cambridge: Cambridge University Press, 1993).
 “Dans cette grande dissonance de la sensible, suivie du corps sonore avec tous ses harmoniques, on offre d’abord à mon oreille tous les dissonnans de la game, purs et sans mêlange; puis le corps sonore avec son cortége, et les uns et les autres dans leur position naturelle, la game partagée rigoreusement en deux portions; d’un côté ce que la nature a produit; de l’autre ce que l’art a imaginé pour la faire valoir et désirer.” Bemetzrieder, Leçons de clavecin et principes d’harmonie (Paris: Bluet, 1771), 340.
Michael Weinstein-Reiman is a doctoral student in music theory at Columbia University. His research interests include keyboard music, technology, gender, aesthetics, and the history of music theory.
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