<P> Jazz has proved to be very difficult to define, since it encompasses a wide range of music spanning a period of over 100 years, from ragtime to the 2010 - era rock - infused fusion . Attempts have been made to define jazz from the perspective of other musical traditions, such as European music history or African music . But critic Joachim - Ernst Berendt argues that its terms of reference and its definition should be broader, defining jazz as a "form of art music which originated in the United States through the confrontation of the Negro with European music" and arguing that it differs from European music in that jazz has a "special relationship to time defined as' swing"', involves "a spontaneity and vitality of musical production in which improvisation plays a role" and contains a "sonority and manner of phrasing which mirror the individuality of the performing jazz musician". In the opinion of Robert Christgau, "most of us would say that inventing meaning while letting loose is the essence and promise of jazz ." </P> <P> A broader definition that encompasses all of the radically different eras of jazz has been proposed by Travis Jackson: "it is music that includes qualities such as swing, improvising, group interaction, developing an' individual voice', and being open to different musical possibilities". Krin Gibbard has provided an overview of the discussion on definitions, arguing that "jazz is a construct" that, while artificial, still is useful to designate "a number of musics with enough in common to be understood as part of a coherent tradition". In contrast to the efforts of commentators and enthusiasts of certain types of jazz, who have argued for narrower definitions that exclude other types, the musicians themselves are often reluctant to define the music they play . As Duke Ellington, one of jazz's most famous figures, said: "It's all music". </P> <P> Although jazz is considered highly difficult to define, at least in part because it contains so many varied subgenres, improvisation is consistently regarded as being one of its key elements . The centrality of improvisation in jazz is attributed to influential earlier forms of music: the early blues, a form of folk music which arose in part from the work songs and field hollers of the African - American slaves on plantations . These were commonly structured around a repetitive call - and - response pattern, but early blues was also highly improvisational . European classical music performance is evaluated by its fidelity to the musical score, with much less discretion over interpretation, ornamentation, and accompaniment: the classical performer's primary goal is to play a composition as it was written . In contrast, jazz is often characterized as the product of group creativity, interaction, and collaboration, which places varying degrees of value on the contributions of the composer (if there is one) and performers . In jazz, the skilled performer will interpret a tune in very individual ways, never playing the same composition the same way twice; depending on the performer's mood and personal experience, interactions with other musicians, or even members of the audience, a jazz musician may alter melodies, harmonies or time signature at will . </P> <P> The approach to improvisation has developed enormously over the history of the music . In early New Orleans and Dixieland jazz, performers took turns playing the melody, while others improvised countermelodies . By the swing era, big bands were coming to rely more on arranged music: arrangements were either written or learned by ear and memorized, while individual soloists would improvise within these arrangements . Later, in bebop, the focus shifted back toward small groups and minimal arrangements; the melody would be stated briefly at the start and end of a piece, but the core of the performance would be the series of improvisations . Subsequent styles such as modal jazz abandoned the strict notion of a chord progression, allowing the individual musicians to improvise even more freely within the context of a given scale or mode . In many forms of jazz, a soloist is often supported by a rhythm section consisting of one or more chordal instruments (piano, guitar, etc .), double bass playing the basslines and drum kit . These performers provide accompaniment by playing chords and rhythms that outline the song structure and complement the soloist . In avant - garde and free jazz idioms, the separation of soloist and band is reduced, and there is license, or even a requirement, for the abandoning of chords, scales and rhythmic meters . </P>

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