Bebop

Bebop or bop is a form of jazz characterized by fast tempos and improvisation based on harmonic structure rather

Bebop or bop is a form of jazz characterized by fast tempos and improvisation based on harmonic structure rather than melody. It was developed in the early and mid-1940s. It first surfaced in musicians' argot some time during the first two years of the Second World War. Hard bop later developed from bebop combined with blues and gospel music.

Many bebop tunes were based on the chord progressions (also called chord changes) from popular songs. (The technical term for such tunes is contrafacts or contrafactions.) A (slightly shortened) version of the chord changes to the song "I Got Rhythm" by George Gershwin was so often used that they are often referred to simply as "Rhythm changes." Contrafaction was already a well-established practice in earlier jazz, but came to be central to the bebop style. In part this was because the extremely fast tempos favored by boppers often did not suit the original melody, and because they often further altered the original chords or even combined chords from two different tunes. In part the use of contrafacts had a practical purpose: small record labels like Savoy, which documented the early bebop movement, often wished to avoid paying copyright fees for pop tunes.