The piano is the only keyboard instrument in which one can grandly vary the effects of the harmonics or overtones of a chord at will by balancing the… - Charles Rosen

The relation of tonic to dominant is the foundation of Western triadic tonality. The attempt of the early nineteenth century to substitute third or mediant relationships for the classical dominant amounted to a frontal attack on the principles of tonality, and it eventually contributed to the ruin of triadic tonality. This ruin was accomplished from within the system, however, as mediant relationships were essential to tonality as conceived in the eighteenth century.

For Beethoven, music was still shape, realized and inflected by instrumental sonority: other realizations may be as absurd as arrangements of the Hammerklavier, for example, always are, but the musical conception takes precedence over its realization in sound. The sonority serves the music. For Schumann, however, as for Chopin and Liszt, the conception was worked out directly within the sonority as a sculptor works directly in clay or marble. The instrumental sound is shaped into music.

The absolutely inaudible is rejected from music during the period of Viennese Classicism in which every musical line is potentially or imaginatively audible, but it makes a dramatic reappearance in the music of Schumann. The most striking of many examples is one of the episodes in the Humoresk, the last of the great piano works of Schumann's early years. ... There are three staves: the uppermost for the right hand; the lowest for the left; the middle, which contains the melody, is not to be played. Note that the melody is no more to be imagined as a specific sound than it is to be played: nothing tells us that the melody is to be heard as vocal or instrumental. This melody, however, is embodied in the upper and lower parts as a kind of after-resonance-out of phase, delicate, and shadowy.