The harmonic rhythm slows at bar 29, with a sustained I chord moving to II in bar 30.In bar 31-32 we have an imitation of bar 27-28, the rhythm and general contour of the right hand melody is the same.
The length of sections sequentially decreases by two bars as shown bellow.
It is worth mentioning that Paul Verlaine’s poem Claire de Lune, which is probably the inspiration for this movement – both the titles Bergamasque and Claire de Lune originate in this poem; is in three stanzas, mirroring Debussy’s use of three sections in this movement.
The composition opens in D major with a tonic chord.
Here Debussy has already broken two rules of conventional voice leading; Debussy begins without the tonic note, introducing it later, where the mediant of the chord (F natural) is doubled.
Throughout the opening phrase the left hand part begins to slowly descend, while the diatonic opening theme floats above in the right hand.
In Bar 2 G and A; an augmented second, show Debussy’s confident use of unconventional intervals.
The right hand chords in this section should be seen as a melody, the harmony is in the bass part of the left hand. While the music feels distinctly diatonic, it does not feel rooted in the tonic key of D minor.
In bar 27 we begin the B section; new thematic material is introduced, as is a change in accompaniment; we now have an arpeggio figure in the left hand. The first two bar phrase uses the rhythmic cell shown earlier to create a melodic phrase. The chord used on the third beat of bar 27, is an unusual harmonic choice within conventional tonality and shows Debussy experimenting with non-functional harmony; this creates a new and interesting sound world, made more obvious by the preceding chord III.
The thematic material in the A and B sections would sharply contrast; which they do here.
An alternative to ternary form could be rounded binary form, again with an added coda.