Relation to Polytonal Music

Definition: The crucial distinction between polytonality (the simultaneous presentation of multiple distinct tonal centers) and Messiaen's modal practice, which creates "the atmosphere of several tonalities at once, without polytonality."

Messiaen's Treatment: Messiaen reiterates that the modes offer listeners the atmosphere of several tonalities at once, without polytonality—a statement previously made in Chapter XVI. The chords and combinations of notes that the modes generate can be made equivocal with polytonal sonorities, but the modal force always absorbs them. By polymodality (discussed in Chapter XIX), multiple modes are superposed, and again, the listener perceives the coexistence of polytonal aggregations completely absorbed by the chosen polymodality.

Modern Context: This represents one of Messiaen's most subtle theoretical distinctions. Polytonality—as practiced by composers like Milhaud, Stravinsky, or Bartók—typically involves simultaneously presenting materials clearly identified with different key areas (for instance, C major in one hand against F-sharp major in the other). The effect is of two or more tonal streams operating independently. Messiaen argues that his modes produce something fundamentally different: because they exist outside any single tonality while containing pitch subsets that suggest multiple tonalities, they create harmonic ambiguity rather than polytonal juxtaposition. The "modal force" absorbs potential polytonal implications, meaning listeners perceive a unified (if ambiguous) harmonic field rather than competing tonal centers.

Contemporary theory might describe this using concepts from neo-Riemannian analysis or pitch-class set theory: the modes function as common ground containing multiple potential tonal interpretations without committing to any single one. An octatonic collection, for instance, contains diminished seventh chords pointing toward four different keys, yet the collection itself doesn't assert any of these keys—it hovers among them. This differs from polytonal juxtaposition, where distinct key areas are simultaneously asserted. The distinction matters aesthetically: polytonality often creates harmonic tension or humor through the clash of incompatible tonalities, while modal ambiguity creates mysteriousness, suspension, or what Messiaen calls "the atmosphere of several tonalities." The promise that Chapter XIX will demonstrate polymodality (superposition of multiple modes) suggests that even when distinct modal layers operate simultaneously, the result still differs from polytonal practice—modes absorb and unify rather than clash and separate.

Examples: Discussed conceptually; demonstrations reserved for Chapter XIX