The Well-Tempered Clavier — Johann Sebastian Bach

Bach's monumental collection of 48 preludes and fugues across all keys, compiled in 1722 and 1742, established the foundation for Western tonal harmony, with each of its 96 movements averaging 4.5 minutes in length. Its systematic exploration of major and minor keys outperforms both Pachelbel's Canon (#7) and Debussy's Clair de Lune (#5) in sheer educational and theoretical significance, shaping the harmonic structure of nearly every subsequent classical work.