Johann Sebastian Bach's 'The Well-Tempered Clavier' proved that keyboards could play in all 24 keys without sounding out of tune.

In the early 1700s, keyboard instruments typically used 'Mean-tone Temperament.' This system prioritized pure thirds in a few keys, but it created a 'wolf interval'—a harsh, howling dissonance—that made keys with many sharps or flats unusable. This limitation restricted composers to a narrow emotional and harmonic range.Johann Sebastian Bach compiled Book I of 'The Well-Tempered Clavier' in 1722 and Book II in 1742. Each volume contains 24 pairs of preludes and fugues, covering every major and minor key in the chromatic scale. By doing this, Bach demonstrated that a 'well-tempered' tuning system allowed for smooth modulation between distant keys without the need to retune the instrument.While modern pianos use 'Equal Temperament' where every semitone is exactly the same distance apart, Bach likely used a variety of 'Well Temperaments' proposed by theorists like Andreas Werckmeister. These systems distributed the mathematical 'comma'—the slight discrepancy in tuning—across the scale. This ensured that while each key had its own unique color or 'flavor,' none were unplayable.This shift was revolutionary for Western music theory and composition. It allowed for the development of the complex harmonies and dramatic key changes found in the works of later masters like Beethoven and Chopin. Bach's work remains the definitive proof that mathematical precision in tuning could unlock total creative freedom for the performer.