Key Concepts

This chapter introduces four key concepts positioning the modes within contemporary compositional practice:

1. Distinction from Traditional Modal Systems - Clarification that Messiaen's modes differ fundamentally from historical modal systems based on scalar traditions transposable twelve times

2. Relation to Atonal Music - The relationship between Messiaen's modes and atonal compositional practices, showing how modes can suggest tonal centers

3. Relation to Polytonal Music - The crucial distinction between polytonality and Messiaen's modal practice, which creates "the atmosphere of several tonalities at once, without polytonality"

4. Quarter-Tone Music - Acknowledgment of theoretical possibility that modes of limited transpositions could exist in microtonal systems, though Messiaen declines to explore this territory