Charlie Parker, Dizzy Gillespie and Thelonious Monk headed a movement of musicians tired of playing the same ``swing'' tunes for dance crowds every night. Often stealing chord progressions from popular songs of the time, the musicians would improvise over the existing harmonic base at blistering tempos. Change-running became the name of the game for bebop musicians, who expanded on the ``vertical'' thinking of swing era musicians with the use of upper-structure chord tensions, most notably the sharp eleventh or tritone. Bebop eventually became obsessed with an incredibly fast, harmonically advanced form of expression that served to be exclusive to all but the most proficient technical instrumentalists. In the end, it was clear that the emphasis was being placed more on technique than on self expression.
In the late 1940's, the West coast community reacted to the Bebop movement with what is now referred to as ``cool jazz''. Later to influence beatniks such as Jack Kerouac and Allen Ginsberg, musicians of the cool period were aloof and individualistic; each existed in his own personal space, and exhibited a certain amount of emotional detachment, understatement and apathy. Although a set of early Miles Davis recordings entitled A Birth of the Cool set the stage for the movement, a high percentage of the cool style players were Caucasian males who brought a number of Europeanisms back into the music. (It is often argued that this a major move on the part of the recording industry.) Later musicians included Zoot Sims, Stan Getz, Dave Brubeck, The Modern Jazz Quartet and Paul Desmond.
As a rejection of these Europeanisms and the emotional detachment of cool artists, African-American musicians sought a return to a more blues oriented context, giving rise to the ``hard bop'' movement. This era was championed by groups led by drummer Art Blakey - embracing the emotional content inherent in the blues while layering it with a jazz context. Instrumentation tended to favor the tenor saxophone, rather than the alto that dominated the bebop period, because of its darker tonal characteristics. Trumpeters such as Lee Morgan and Freddie Hubbard served as models for ``hard'' jazz musicians in every sense of the word.
In 1959, certain circles of musicians began to express discontent with the current state of jazz music. Many believed that in order to progress, a complete removal of melodic, harmonic and rhythmic traditional concepts would be the order of the day - freeing once and for all the music from European stylistic considerations.
Appropriately, in 1959, Ornette Coleman released The Shape of Jazz to Come, laying the framework for a decade of chaos.