Chapter XIX: Polymodality
Original: Pages 68–70 in Satterfield translation
Musical Examples:
Overview
Chapter XIX concludes the treatise's harmonic section by presenting polymodality—the superposition of multiple modes of limited transpositions operating simultaneously in different voices or textural layers. This technique represents the culmination of Messiaen's modal practice, demonstrating how the modes can be combined to create complex harmonic textures while maintaining the clarity and distinctive character of each constituent mode. The chapter emphasizes that in polymodal passages, each staff uses its assigned mode both melodically and harmonically, with all notes belonging to that mode. Messiaen explores polymodal combinations systematically, beginning with two superposed modes, advancing to three-mode superpositions, and concluding with polymodal modulation where the modal combinations themselves change over time. Throughout, the chapter demonstrates that polymodality differs fundamentally from polytonality: rather than creating the clash of incompatible key areas, superposed modes produce unified harmonic fields with distinctive coloristic properties, their "modal force" absorbing potential polytonal implications into coherent sonic atmospheres.