Overtones. That's what happened when the piano was invented. Overtones became the subject of the music and the content of the sound, not discrete notes or harmonies. That's why there are so many broken "chords" in the left hand: the harmonic context shifts gradually as overtones compound upon already sounding mixes of sound. That's why the "bass" notes in a broken chord are not to be sustained and why they do not indicate full change of pedal: they are specifically crafted to carry over and blend with an already sounding constellation of vibrations. Visual analysis often obscures this essential auditory observation.

In much piano music one cannot--must not--separate functions in the Baroque manner of bass, melody and chord. Doesn't work.