Abbreviated Analysis: Debussy’s “La Cathedrale Engloutie”
The introduction runs from m. 1 through m. 15, and may be further divided into three sub-sections: subsection A (mm. 1 – 6), subsection B (mm. 7 – 12), and subsection C (mm. 13 – 15). Subsection A functions as an introductory presentation of the thematic idea of the piece; it also establishes a static grouping of notes (a series of rising parallel chords on the open fifth and octave) that are focused around the pentatonic collection of G-D-E-A-B pitches. The pentatonic groupings resurface throughout the piece, and can themselves be thought of as a harmonic motive. Subsection B functions as a tonal transition, modulating in key and foreshadowing the ideas in Section III; and subsection C reaffirms the rising parallel chords and the idea of a pentatonic collection of pitches.
Section I begins on m. 16 and runs through m. 27, again playing with pentatonic groupings and similar progressions of rising chords. It features a transition at mm. 22 – 27 into Section II, which itself runs from mm. 28 – 41 and features a progression of parallel triadic chords. Measures 42 - 46 begin another key transition into C# minor. Section III runs mm. 47 – 67 and explores the key of C# minor; it takes up the foreshadowing in subsection B of the introduction, then follows another key transition (mm. 68 – 71) into Section IV, which takes up the parallel triadic chords once more, in C major. The piece ends with a coda-like figure from m. 84 - 89, which, as stated in the written musical direction, is “…in the sound of the beginning”, revisiting the rising parallel chords and the same general pentatonic grouping of G-D-E-A-B.
In summary of segmentation, the piece follows an almost poetic form - Intro, A, B, A’, C, Coda; this supports my personal conception of the prelude as an atmospheric tone poem. The work is highly programmatic, and I divided the sections based on the sonorities of the piece as they changed or were varied; I also considered the segments in terms of modulations of key, motive, and texture. The key center, I believe, is C major, while there are a few modulations on transitional keys heading to and from C#. The harmonic motive of the rising parallel chords resurfaces in some form in every section of the piece; throughout, the one constant interval is the perfect octave, and though the meat of the chords change from fourths/fifths to triadic intervals depending upon the section, the octave seems to be the basis for the piece’s atmospheric, open sound. The chords become denser the further along the piece progresses, which might represent the sinking of the cathedral into the murky, heavier depths, and the sense of timbre changes as well.
Debussy takes the material and, by limiting himself to mostly parallel progressions and wandering harmonies, creates a static grouping of tonal yet nonfunctional sonorities that are varied from section to section, thus providing variety in unity throughout his prelude.