Because it spans music from Ragtime to the present day – over 100 years now – jazz can be very difficult to define. Attempts have been made to define jazz from the perspective of other musical traditions – using the point of view of European music history or African music for example – but jazz critic Joachim Berendt argues that all such attempts are unsatisfactory. One way to get around the definitional problem is to define the term "jazz" more broadly. Berendt defines jazz as a "form of art music which originated in the United States through the confrontation of blacks with European music"; he argues that jazz differs from European music in that jazz has a "special relationship to time, defined as 'swing'", "a spontaneity and vitality of musical production in which improvisation plays a role"; and "sonority and manner of phrasing which mirror the individuality of the performing jazz musician".
Travis Jackson has also proposed a broader definition of jazz which is able to encompass all of the radically different eras: he states that it is music that includes qualities such as "swinging", improvising, group interaction, developing an 'individual voice', and being 'open' to different musical possibilities". Krin Gabbard states that “jazz is a construct” or category 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”.
While jazz may be difficult to define, improvisation is clearly one of its key elements. Early blues was commonly structured around a repetitive call-and-response pattern, a common element in the African American oral tradition. A form of folk music which rose in part from work songs and field hollers of rural Blacks, early blues was also highly improvisational. These features are fundamental to the nature of jazz. While in European classical music elements of interpretation, ornamentation and accompaniment are sometimes left to the performer's discretion, the performer's primary goal is to play a composition as it was written. In a 1975 film, pianist Earl Hines said,
... Now when I was playing classical music I wouldn’t dare get away from what I was reading. If you’ve noticed, all of the symphonic musicians, they have played some of those classical tunes for years but they wouldn’t vary from one note – and every time they play they have to have the music. So that’s why for some classical musicians, it’s very difficult for them to try to learn how to play jazz.
In jazz the skilled performer will interpret a tune in very individual ways, never playing the same composition exactly the same way twice. Depending upon the performer's mood and personal experience, interactions with fellow musicians, or even members of the audience, a jazz musician/performer may alter melodies, harmonies or time signature at will. European classical music has been said to be a composer's medium. Jazz, on the other hand, is often characterized as the product of egalitarian creativity, interaction and collaboration, placing equal value on the contributions of composer (if there is one) and performer, 'adroitly weigh[ing] the respective claims of the composer and the improviser'.
The jazz soloist is often supported by a rhythm section who "comp" (accompany the soloist), by playing chords and rhythms that outline the song structure and complement the soloist. In 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—many early jazz performers could not read music. Individual soloists would improvise within these arrangements. Later, in bebop the focus shifted back towards small groups and minimal arrangements; the melody (known as the "head") would be stated briefly at the start and end of a piece but the core of the performance would be the series of improvisations. Later styles of jazz 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. The avant-garde and free jazz idioms permit, even call for, abandoning chords, scales, and rhythmic meters.