Chopin's Nocturne Op. 9 N. 3 in B major is one of the most complex. Its greatest peculiarity is the harmonic ambiguity that derives from the continuous oscillation between the tonality of B major and B minor.
From the very first bar, this continuous oscillation between these two distant tonality does not allow us to clearly focus on the mood of the piece.
A piece that, if it had been written by John Field, inventor of the Nocturne genre, would probably have remained more banally fixed in the key of B major.
To make this ambiguity and instability heard, to make it perceived, we must not smooth out the dissonances, the harmonic surprises but, on the contrary, we must make them evident.
This is a complex music, it is not monochord, it does not have a single idea to express, but it lives on a multiplicity of aspects that all together make it so special and unique.
Therefore the dissonances given by the internal voices must always be clearly perceptible.
For example, the voice of the left hand, very well indicated by Chopin through upward stems on the notes, is an equally important voice, because it becomes a counterpoint that creates a somewhat poignant tension with the melody.
By analyzing and realizing Chopin's original writing well, details emerge that make the music even richer, even more real and evidently close to what the author wanted to express.
They are indeed very dissonant intervals, which to many pianists might seem too "hard" to emphasize, fearing almost to "ruin" the cantabile of the melody.
But this is precisely a cantabile that must be a little "dirty" with this dissonances, to make us perceive its particular harmonic instability and inimitable, indescribable beauty.
Photo: Chopin Nocturnes, First edition, Fr. Kistner, Leipzig, 1833