The “pentatonic-ish-ness” of La fille is, indeed, more
than a fingerprint but bears novel structural possibilities
with respect to Schenkerian models, chiefly the interrupted
Ursatz. To equate this piece, as did Kopp (quoted earlier)
with Chopin’s black-key Etude—both “operating within a
diatonic framework”—is to overlook the profound and
transformative implications of pentatonicism in the hands
of Debussy. (Unlike La fille, the Etude expresses a strong
dominant-tonic polarity and reduces clearly to an orthodox
Schenkerian 3-line, thus truly manifesting what we normally
mean by “diatonic tonality.”34) What is interesting about La
fille is not the degree to which the pentatonicism in the piece
is (or is not) systematized (apparently Kopp’s concern), but