Free jazz emerged in the 1950s as a rebellion against jazz conventions. Its meter is fluid, its harmonies unfamiliar, sometimes atonal. Song structures may be experimental and unpredictable. A key element in free jazz is collective improvisation — riffing done not just by a featured soloist, but by a whole group of musicians playing together. To prepare for adventures in the days ahead — which will resemble free jazz — listen to its pioneers: Ornette Coleman, Charles Mingus and Sun Ra. Don’t fall prey to scapabobididdilywiddilydoobapaphobia, a fear of freestyle jazz.