Studies of harmonic dualism have traditionally focused on German-speaking theorists, particularly Moritz Hauptmann, Arthur von Oettingen, and Hugo Riemann (Harrison 1994; Clark 2001; Rehding 2003; Klumpenhouwer 2011). Recent scholarship, however, has worked to decenter the German triumvirate, recognizing harmonic dualism as a wider European movement with significant contributions from France, Italy, Scandinavia, Czech lands, and beyond (Gjerdingen 1995; Rehding 2009; Kieffer 2016; Utne-Reitan 2022; Locanto 2023; Carrozzo 2024; Kirkegaard 2024; Lill 2024; Venturino 2024).

This paper examines dualisms from Belgian and Dutch theorists Emile Ergo (1891a–f, 1897, 1914), J. H. Garms Jr. (1906), and Antoine Auda (1930)—approaches left largely undiscussed in the music-theoretical literature (Holtmeier 2011; Rehding 2025). Beyond pluralizing our music-historical accounts, the study of their methods also helps broaden our understanding of dualism’s very nature. I argue that dualism is not a monolithic framework extending uniformly across all musical domains: rather, it can be applied selectively to triad generation, scales, harmonic function, and other musical objects.

Ergo, Garms Jr., and Auda all present “hard” dualist accounts of triadic structure—that is, they equate major and minor triads through inversional symmetry, not through a “soft” explanation of the triads as “two distinct but equal expressions of a single structuring principle” (Klumpenhouwer 2011, 196). However, they diverge in their other music-theoretical explanations, often embracing monism. Ergo offers hard dualist accounts of triadic generation and scale formation; while initially employing hard dualist harmonic functions, he reverts to monist function labels in his later work. Garms promotes monist functions while using hard dualist methods to generate triads and various chromatic sonorities. Auda includes hard dualist triad generation and monist scale constructions: his C major and minor scales both ascend and feature different intervallic patterns.

These Belgian and Dutch approaches help expand our notion of dualism beyond the conventionally German-centric narrative. They also encourage a more flexible understanding of dualism: “hard” dualism often governs some musical domains while “soft”—or even monist—methods direct others. In closing, I reflect on how our discipline might reassess dualism, viewing it not as an all-or-nothing system, but as an adaptable toolkit with diverse implementations.

Czech music theory in the twentieth century includes a tradition of theorizing harmonic function, represented by Otakar Šín (1881–1943), Karel Janeček (1903–1974), Karel Risinger (1920–2008), and Vladimír Tichý (b. 1946). By examining their approaches, I will argue that harmonic dualism is not a singular conceptual framework but a flexible one, which can be applied in various ways and to varying degrees—“hard” or “soft” (Klumpenhouwer 2011)—to a variety of musical phenomena. The persistence of dualism in Czech theories of harmonic function also suggests that the two concepts may be more closely linked than both practitioners and historians of harmonic function have previously explored.

I discuss three ways that dualism manifests itself in Czech music theory. I call the first “vestigial dualism:” elements of Hugo Riemann’s dualism (1883) that have persisted in Czech theories of harmonic function, despite the authors’ uniform rejection of his dualist view that the minor triad is generated downward from its fifth. Šín, for instance, maintains Riemann’s dualist view that, in minor, the natural progression involves the dominant moving to the subdominant. Thesecond manifestation consists of more novel instances of dualism. Risinger, for example, suggests that the dual of the dominant function chord should not be the minor subdominant, as is typical, but instead a minor triad built on the subtonic, because it inverts the typical voice leading of the dominant triad. Third is a trend of Czech theorists correlating dualism more broadly with symmetry and inversion (Dušek 1980).

The work of these Czech theorists illustrates that dualism need not be an all-subsuming principle, but that it can be applied selectively and in conjunction with non-dualist thinking. Further, the overwhelming persistence of dualism in Czech theories of harmonic function suggest the need for reevaluating the relationship between dualism and harmonic function.

While typically viewed as a hopelessly impractical curiosity, harmonic dualism has recently received renewed attention by contemporary musicians, who know it as “negative harmony” after Steve Coleman, and especially Jacob Collier. My presentation considers this phenomenon from two perspectives: 1) a historical or epistemological perspective, which investigates just how much harmonic dualism has to do with negative harmony; and 2) a public music theory (PMT) perspective, which explores what is communicated and what is lost when a theory of harmony becomes a compositional tool. The historical/epistemological perspective has already been taken up to some degree by Debora Haller (2020), but Haller ignores the significant role that basic post-tonal theory concepts—specifically pitch inversion and chromatic wedges—plays in Collier and Coleman’s conceptions of negative harmony. In understanding the newfound interest in negative harmony as an instance of PMT, I explore the ways in which the focus on practicality and utility ironically reveals a bias towards monism, and replicates many of the complaints about dualism lodged by the theory’s historical critics.