A Comparison of two 20th Century Pieces

January 05, 2021 Jack L

A deep dive into the form, structure, harmony and tonality of Debussy's Nuages and Poulenc's Trio for Piano, Oboe and Bassoon (iii mov).

The structure of Debussy’s Nuages is interpreted by musicologists in two different ways. The first of which is a structure of five rotations. Each rotation contains two main musical motifs, say ‘A’ and ‘B’. The fourth rotation has a third idea ‘C’ in the middle of it. The first rotation begins at bar 1, the second at bar 11, third at bar 33, fourth at bar 57 with the ‘C’ idea commences at bar 64 and ends after bar 79 and finally the fifth at bar 94 ending at the end of the piece at 102. The A and B ideas in question are both presented in the first rotation in the following places. The ‘A’ motif is a flowing crotchet idea in 6/4 time which is presented at bar one in the clarinets and bassoons and ends at the end of bar 4. The ‘B’ motif in 4/4 time is presented in the Cor Anglais in bar 5 to 8. The alternative way musicologists may view the structure of this piece is as a Ternary form piece (ABA’). The first three rotations and part of the fourth before the ‘C’ idea enters (bars 1 to 63) all form the first A section of the ternary form. The ‘C’ idea in the fourth rotation then becomes the B section of the Ternary form at bars 64-79. The A’ section begins at bar 80 and finishes at the end of the piece at bar 102.


The structure of Mvt II of Poulenc’s Trio for Piano, Oboe and Bassoon is in a ternary form (ABA’) structure. The section begins at bar 1 and ends at bar 22. The idea that distinguishes this from the B section is the extensive featuring of the theme that is first presented in the top voice of the left hand of the piano at bars 1-4. The B section commences at bar 23 and ends at bar 34. The main melodic motif that is developed throughout this section is first presented in the Oboe at bar 23-24. The A’ section begins at bar 34 and reintroduces the theme form bar 1-4 as the main point of melodic exploration. The A’ section then lasts until the end of the piece at bar 64.


Debussy’s use of phrase lengths varies substantially throughout the movement. The first four bars present (according to the five-rotational interpretation) the ‘A’ motif. This phrase is balanced by another 4-bar phrase from bar 5-8 which presents the ‘B’ motif. It could be argued that Debussy uses bars 7-10 as a means of transitioning between slow chords, rather than a musical phrase in the traditional sense. Between bars 11 and 20 the phrasing is ambiguous. It could be viewed 3, 3 and 4 bar phrases (11-13, 14-16 and 17-20). Debussy returns to more clear phrasing afterwards 21-25 and 26-29 form two clear four-bar phrases. In the ‘B’ section (according to the ternary form interpretation) the flute enters with a 3-bar phrase from 64-66 and then a four-bar phrase from 67-70. These two phrases are clearly distinguished by phrase markings in the harp and slur markings in the flute. From these select examples, it’s clear that Debussy intentionally uses both balanced 4 and 8 bar phrasing in places and unbalanced phrase lengths of 3 or 7 bars throughout the movement. It is worth noting, however, that Debussy never disrupts a phrase by changing the base metre of 6/4, unlike Poulenc in his Trio.


Poulenc's use of phrases is generally more balanced than Debussy. Poulenc composes the movement generally of 2, 4 and 8 bar phrases. However, Poulenc alters these in multiple ways. For instance, in bar 8, the second four-phrase is cut short by a quaver through the use of a 3/8 rather than 2/4 time signature in the last bar. From bars 9-33, all of the music is in regular 2 and 4 bar phrases. At bar 38, the start of the next phrase is slightly ambiguous. It could be seen that there are 2 3 bar phrases at 35-37 and 38-40. It could also be interpreted as 3 lots of 2 bar phrases at 35-36, 37-38 and 39-40. At bar 41, clear 2 and 4 bar phrases are restored until bar 50. At bar 50, a 2/8 bar is used which extends the would-be 2 bar phrase starting at 49 to 3 bars (or equivalent to 2 and a half bars in 4/8). 


Debussy's use of tonality is advanced and often ambiguous. Debussy creates a B minor feel in the opening four bars by firstly introducing B and F# as a dyad on the first crotched giving a strong indication of a mode or key based around B, and then composing the top melodic line (played by first clarinet and first bassoon) using the degrees 2, 3, 4 and 5 of the B minor scale. The tonality is coloured by the use of an octatonic scale in the lower melodic line (played by 2nd clarinet and 2nd bassoon). Debussy sometimes suddenly changes between different tonal centres, for instance at bar 19 Debussy shifts to a B-flat Dorian mode up from a D pentatonic feel at bar 17-18. At bar 33-37, the use of tonality appears ambiguous because of octave scoring in the strings and chromatic lines in the upper woodwinds. At bar 42-50, the tonality is based around B but octatonic scales are used, meaning a distinct major or minor feel is lacking. At bar 64 to 70, a clear D# Dorian feel is created through the string chordal accompaniment which plays a D# minor chord at bar 64, then a G# major chord at 66which brings out the raised 6th (B#). From bar 80-102, the tonality again revolves around the octatonic scale on B, and is therefore often lacking in a clear major or minor feel. Towards the end of the piece at bar 99-102, the strings gradually resolve onto a unison B, making clear that the movement is based around B, although perhaps lacking a distinct minor or major feeling because of the extensive use of the octatonic scale to create melodies and chords.


Poulenc’s use of tonality is significant in that he modulates through a multitude of different keys throughout the movement. Poulenc does however maintain many elements of traditional functional harmony in many instances. For example, the movement firmly establishes the key with a clear B flat major chord played in the piano in bars 1 and 2. Although shifting to a major chord on the flat 6th (G flat major) at bar 3, he maintains the tonal centre through the use of a tonic pedal. The second four-bar phrase (5-8) phrase moves the tonality towards F major by introducing a major chord II (C major) which functions as the V chord of F major. A perfect cadence in the dominant is then completed with the instance of an F major chord at bar 8. It is worth noting here that Poulenc’s use of tonality in the first 8 bars is traditional to an extent in that he has modulated to the dominant by the end of an 8-bar phrase. Poulenc does however use frequent modulations in places. For instance a V7-I cadence in E flat major (the subdominant of the home key B flat major) in bar 11, then V7-I in D flat major in bar 12, and then IV-V-I in a flat major in bar 14, in which the A flat major chord becomes V of D flat major, which arrived at bar 15. In bar 17, A minor is suddenly introduced after a D flat major chord in bar 16. The A minor chord functions as IV of E minor because B major is introduced in 172 which leads to a perfect cadence in E minor at bar 18. One final important point is the way that Poulenc has ended the movement. Despire starting out in B flat major, Poulenc ends the movement in F minor. This clearly is an undermining of the commonality of movements ending in the same key or relative major (if starting minor) as where they begin.


Debussy explores harmony in multiple ways throughout the movement. The most notable feature of the movement is the extensive use of non-functional harmony by directly transposing chords up and down, even if they would serve a functional purpose in traditional functional harmony. The first instance of this can be seen at bar 14 in which 6 chords which would conventionally be dominant 9th chords are played, each one a direct transposition down from the other. A similar technique can be seen at bar 29-30 in which simple triads are directly shifted down by perfect 4ths or up or down major 2nds. However, they are not all directly transposed because Debussy keeps all of the notes of B natural minor, hence creating both major (for instance D major at 294) and minor chords (such as F# minor at 292). Another notable feature is the use of the octatonic scale to build up harmonies. An instance of this can be seen at bar 42, in which 6 chords are played that are all composed up of notes from B flat octatonic, creating both minor (eg 421) and ambiguous (eg A flat, D and G flat at 422). Debussy also sometimes uses harmony very simply, for instance, a long held D# minor chord at bar 64, which changes to a G# major chord at 656.


Poulenc’s use of harmony differs to Debussy in several ways. Firstly, Poulenc uses parallelism much less frequently than Debussy. The only clear instance of it is in the use of German 6ths or Dominant 7ths (depending on interpretation!) In a descending sequence of minor thirds in bar 30 in the piano. Other than that, Poulenc's use of harmony is functional. For instance, the first 8 bars of the movement feature instances of functional harmony. The C major chord that is introduced in 5then functions as V of F major in bar 7. A modulation to the dominant key is then completed at bar 8. The F major chord at bar 8 then functions as a V of B flat to return to the home key in bar 9. This use of harmony is entirely functional. Poulenc does, however, use many altered chords and chords outside of the key. For instance, bar 3 features a major chord on the flat 6th of B flat major (G flat major). Another example is at bar 34 in which F# is in the base, but the F#(7) chord that should be used to have a perfect cadence in B is altered significantly in that there is a minor 9th (G) and a flat fifth (C) in the chord, but no normal fifth or third until the final quaver of bar 34 in the piano left hand (C#) and oboe (A#).


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