Chapter 1

Ay me! what warbles yields mine instrument!
The basses shriek as though they were amiss!

-William Percy, "Coelia" (1594)

The piano is perhaps the most generous instrument ever invented. Its range, from bass to treble, is as large as an orchestra's. It allows ten tones-sometimes even more-to be struck simultaneously, and holds them in the air at a pianist's will. The piano can growl and sing and beat time. It can render arid fugues and impressionist waterfalls with equal naturalness. And, unlike the ungrateful French horn or the finicky oboe, if you keep it in tune, it will be an obedient servant. But the principle that truly underlies the piano's versatility is hidden beneath the geometry of its white and black keys.

Clusters of two blacks, then three, then two, and so on, form a repeating pattern above a solid row of whites. When one's eye has become accustomed to the terrain, the alternating groupings signal the names of each note on the keyboard. There are only twelve different ones (each tied to a letter of the alphabet), and in our modern tuning they are built in equidistant steps, like a well-made ladder.

This arrangement produces wondrous results: Through it, a Chopin prelude can gently weep across the keys; Debussy's perfumed phrases can swirl in gentle clouds; Webern can set in motion intricate strings of melody, like threads of glistening pearls.

All of this is possible only because the modern keyboard is a design in perfect symmetry-each pitch is reliably, unequivocally equidistant from the ones that precede and follow it. This tuning allows a musical pattern begun on one note to be duplicated when starting on any other; it...