Relationship to Other Chapters

Chapter XVI represents the theoretical keystone of the treatise's harmonic section, with connections radiating throughout the entire work. The modes were anticipated in Chapter I's "charm of impossibilities," where Messiaen first articulated the aesthetic principle underlying symmetrical structures. Specific chords discussed in Chapter XIII (added notes) and Chapter XIV (chord on the dominant, chord of resonance, chord in fourths) are revealed as derivable from particular modes—the added sixth and augmented fourth chord belongs to Mode 2, the chord of resonance connects to Mode 3, and the chord in fourths derives from Mode 5. Chapter XV's pedal groups, passing groups, and embellishment groups can all operate within modal contexts, as demonstrated in several examples.

The fundamental parallel between modes and nonretrogradable rhythms (Chapter V) establishes the systematic unity of Messiaen's entire compositional approach, demonstrating how a single structural principle—symmetry—generates both rhythmic and harmonic materials. Melodic formulas discussed in Chapter X are revealed as mode-specific, with particular contours associated with particular modes (Mode 5 with its characteristic melodic formula, Mode 6 appearing in "les Bergers" and "la Vierge et l'Enfant"). The chapter anticipates Chapter XVII (modulations of the modes), Chapter XVIII (relation to modal, atonal, polytonal, and quarter-tone music), and especially Chapter XIX (polymodality), where combinations of different modes will create complex coloristic effects. Throughout the remaining chapters, the modes function as the primary harmonic vocabulary, demonstrating their centrality to Messiaen's compositional language.