The Well-Tempered Clavier, Book 1

A prelude is a short, often improvisatory-sounding instrumental piece that traditionally precedes another work or sets a tonal and expressive atmosphere on its own. Emerging in the early Baroque era from the practice of freely extemporizing before a liturgical or secular performance, the prelude evolved from unmeasured lute and keyboard introductions into highly crafted pieces for organ, harpsichord, and later piano. In the 19th century it became an autonomous character piece (e.g., Chopin’s Op. 28), while in the 20th century composers explored cyclic sets across all keys and a wide range of styles (Debussy, Rachmaninoff, Shostakovich). Despite its brevity and flexibility, the prelude typically establishes a key or mode, a figuration pattern, and a distinct mood, favoring clear tonal focus, continuous flow, and a compelling gesture over strict formal constraints.