The prelude La Cathédrale engloutie (The Sunken Cathedral) is inspired by a myth:

"This piece is based on an ancient Breton myth in which a cathedral, submerged underwater off the coast of the Island of Ys, rises up from the sea on clear mornings when the water is transparent. Sounds can be heard of priests chanting, bells chiming, and the organ playing, from across the sea."

Hutcheson, Ernst, The Literature of the Piano (New York: Knopf, 1981), 314

• Debussy begins with a series of chords using fourths and fifths (A). The left hand in a low register, far apart from the right hand in a high register. This separation gives a particular color to these chords. Imitation of the organ of which the myth speaks?
• The chords of the left-hand go down by degrees (G-F-E), the right-hand holds the notes D-G-D.
• Above these chords appears a melodic motif (B) doubled by fourths and fifths.

Paavali Jumppanen, piano
Isabella Stewart Gardner Museum
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Priests chanting?

A first thematic material (A) is developed in measures 7 to 13. We will identify it as the first theme.

• The melody is doubled in octaves and accompanied by an E pedal note (bells chiming?).
• The first theme is based on the melodic motif of the first bars.
• The tonic of this scale or mode is not clear. If we use the pedal note E, we have a Lydian mode (B).
• At bar 13, the left-hand chords move down until they reach C at bar 14.
• At measures 14 and 15, the melodic motif from the first few measures reappears.

Paavali Jumppanen, piano
Isabella Stewart Gardner Museum
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Little by little coming out ...

• Debussy indicates Peu à peu sortant dans la brume (little by little coming out of the mist). The use of eighth notes triplets helps dissolve the mist.
• Measures 16 through 19 use the B-pentatonic major scale.
• The B chord with the ninth and thirteenth (omitting the seventh), is the result of all the scale notes.
• The quarter note chords use the melodic motif.

Paavali Jumppanen, piano
Isabella Stewart Gardner Museum
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... in the mist

In measure 19, we move to an E-flat major chord, the intensity increases:

Paavali Jumppanen, piano
Isabella Stewart Gardner Museum
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Canon

In measure 22, Debussy develops the melodic motif in canon form:

Paavali Jumppanen, piano
Isabella Stewart Gardner Museum
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Second theme

The canon takes us to the climax of the prelude with ff dynamics.

• A second theme appears.Although based on the same melodic motif as the first theme, we consider it a new theme due to its contrasting character
• Major and minor triads double the upper voice in parallel motion over a C pedal.
• The mode used by the upper melodic line is Mixolydian.
• When harmonizing the upper voice, Debussy sometimes uses the B natural to maintain perfect chords.

Paavali Jumppanen, piano
Isabella Stewart Gardner Museum
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Back into the mist?

• Debussy insists on the first notes of the theme (G-A-C), first in melodic form in measures 40 and 41, then as chords in bars 42 to 45.
• The bass follows the downward movement that began in the first few bars. It moves from C to B flat (measures 42 and 43) until it reaches A-flat (measure 44).
• A-flat is enharmonically transformed into G sharp to set up the next section.

Development of the first theme

• The first theme now appears more developed over a sustained G pedal tone.
• It uses the notes of the E Lydian mode again.
• From measure 62 to 67, a series of dominant seventh chords harmonize the melody.
• We rest on the dominant G sharp chord at bar 67.
• At measures 68 and 69, the B-sharp of the G-sharp chord transforms enharmonically to C natural.
• The natural C will serve as a common note to connect with the next section.

Paavali Jumppanen, piano
Isabella Stewart Gardner Museum
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Final measures

• The notes F# - G# - C takes us to the final section.
• We heard the second theme for the last time over a C pedal.
• We end with the melodic motif of the first bars.

Paavali Jumppanen, piano
Isabella Stewart Gardner Museum
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Complete Prelude

Paavali Jumppanen, piano
Isabella Stewart Gardner Museum
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