section_path: Elements/Improvisation
section_name: Improvisation
paragraph_text: Improvisation
  
  Although jazz is considered difficult to define, in part because it contains many subgenres, improvisation is one of its defining elements. The centrality of improvisation is attributed to the influence of earlier forms of music such as blues, a form of folk music which arose in part from the work songs and field hollers of African-American slaves on plantations. These work songs were commonly structured around a repetitive call-and-response pattern, but early blues was also improvisational. Classical music performance is evaluated more by its fidelity to the musical score, with less attention given to interpretation, ornamentation, and accompaniment. The classical performer's goal is to play the composition as it was written. In contrast, jazz is often characterized by the product of interaction and collaboration, placing less value on the contribution of the composer, if there is one, and more on the performer. The jazz performer interprets a tune in individual ways, never playing the same composition twice. Depending on the performer's mood, experience, and interaction with band members or audience members, the performer may change melodies, harmonies, and time signatures.
  
  In early Dixieland, a.k.a. New Orleans jazz, performers took turns playing melodies and improvising countermelodies. In the swing era of the 1920s–'40s, big bands relied more on arrangements which were written or learned by ear and memorized. Soloists improvised within these arrangements. In the bebop era of the 1940s, big bands gave way to small groups and minimal arrangements in which the melody was stated briefly at the beginning and most of the piece was improvised. Modal jazz abandoned chord progressions to allow musicians to improvise even more. In many forms of jazz, a soloist is supported by a rhythm section of one or more chordal instruments (piano, guitar), double bass, and drums. The rhythm section plays chords and rhythms that outline the composition structure and complement the soloist. In avant-garde and free jazz, the separation of soloist and band is reduced, and there is license, or even a requirement, for the abandoning of chords, scales, and meters.