What has 88 keys but can't open a single door?

The classic riddle "What has 88 keys but can't open a single door?" cleverly points to a piano. While we typically associate "keys" with opening locks, the keys of a piano serve an entirely different purpose: creating music. A standard modern piano is equipped with 88 keys, a configuration that has been widely adopted since the 1890s to provide musicians with a comprehensive range of notes and tones. These keys, 52 white and 36 black, are arranged to cover seven full octaves plus a minor third, allowing for a vast spectrum of musical expression.

The piano's invention is credited to Bartolomeo Cristofori of Padua, Italy, around the year 1700. Cristofori, an expert harpsichord maker, developed an instrument that could produce both soft and loud sounds, a significant improvement over earlier keyboard instruments like the harpsichord. He originally named it "gravicembalo col piano e forte," meaning "harpsichord with soft and loud," which was eventually shortened to "pianoforte" and then simply "piano." When a key is pressed, a felt-covered hammer strikes a string, causing it to vibrate and produce a sound, a mechanism that classifies the piano as both a string and a percussion instrument.

The 88 keys on a piano enable it to achieve the widest tonal range of all instruments, capable of playing notes lower than a double bassoon and higher than a piccolo. This extensive range covers what is considered the musically significant spectrum of human hearing. Historically, piano keys were famously made from ivory, sourced from elephant tusks, leading to the phrase "tickle the ivories." However, since the 1950s, to protect wildlife, modern piano keys are predominantly manufactured from plastic and other synthetic materials, while still retaining the traditional black and white appearance.