5. The sustain pedal enables pianists to play
musical passages that would otherwise be
impossible, such as sounding a 10-note
chord in the lower register and then, while
this chord is being continued with the
sustain pedal, shifting both hands to the
treble range to play a melody and arpeggios
over the top of this sustained chord. Unlike
the pipe organ and harpsichord, two
major keyboard instruments widely used
before the piano, the piano allows
gradations of volume and tone according to
how forcefully a performer presses or
strikes the keys.