Defining the essence of free jazz is complicated; many musicians draw on free jazz concepts and idioms, and free jazz was never entirely distinct from other genres. Many individual musicians reject efforts at classification, regarding them as useless or unduly limiting. Free jazz uses jazz idioms, and like jazz it places an aesthetic premium on expressing the "voice" or "sound" of the musician, as opposed to the classical tradition in which the performer is seen more as expressing the thoughts of the composer.
- Many free jazz musicians, notably Pharoah Sanders and John Coltrane, use harsh overblowing or other techniques to elicit unconventional sounds from their instruments, played unusual instruments like the shehnai, or used recording techniques like Marzette Watts.
- Earlier jazz styles typically were built on a framework of song forms (e.g.: the twelve-bar blues or the 32-bar AABA popular song form) with a set framework of chordchanges. In free jazz, the dependence on a fixed and pre-established form is eliminated, and the role of improvisation is correspondingly increased. As guitaristMarc Ribot has remarked, free jazz musicians like Ornette Coleman and Albert Ayler, "although they were freeing up certain strictures of bebop, were in fact each developing new structures of composition."
- Free jazz, especially during its inception, contains theme of both progressive musical language and gathering inspiration from the past. The rejection of the bop aesthetic was combined with an increased fascination with earlier styles of jazz such as Dixieland jazz with its collective improvisation, as well as African music. This interest in older and more culturally authentic forms of music resulted in the incorporation of instruments from a variety of global cultures by many free jazz musicians from a variety of global cultures. This includes Ed Blackwell's use of the West African talking drum, and Leon Thomas's interpretation of pygmy yodeling.
- Typically this kind of music is played by small groups of musicians, although some examples use larger numbers. For example, John Coltrane's 1965 albumAscension, uses eleven musicians.
- Other forms of jazz use clear regular meters and strongly pulsed rhythms, usually in 4/4 or (less often) 3/4. Free jazz normally retains a general pulsation and often swings but without regular meter, and we encounter frequent accelerando and ritardando, giving an impression of the rhythm moving in waves. Despite all of this, it is still very often possible to tap one's foot to a free jazz performance; meter is more freely variable but has not disappeared entirely.
- Previous jazz forms used harmonic structures (usually cycles of diatonic chords), and even when improvisation occurred it was founded on the notes in the chords. Free jazz almost by definition is free of such structures, but also by definition (it is, after all, "jazz" as much as it is "free") it retains much of the language of earlier jazz playing. It is therefore very common to hear diatonic, altered dominant and blues phrases in this music.
- The practitioners of free jazz were serious about pursuing this approach, and their music employed concurrent developments in 20th Century art-music theory and practice also used by John Cage, Musica Elettronica Viva, and the Fluxus movement.
- Finally, some forms use composed melodies as the basis for group performance and improvisation. Free jazz practitioners sometimes use such material, and sometimes do not. In some music which is called "free jazz" (or avant-garde jazz) other compositional structures are employed, some of them very detailed and complex; recordings of Clifford Thornton and Anthony Braxton furnish many examples.
Many critics, particularly at the music's inception, suspected that the abandonment of familiar elements of jazz pointed to a lack of technique on the part of themusicians. Today such views are more marginal, and the music has built up a tradition and a body of accompanying critical writing. It remains less commerciallypopular than most other forms of jazz.
This breakdown of form and rhythmic structure has been seen by some critics to coincide with jazz musicians’ exposure to and use of elements from non-Western music, especially African, Arabic, and Indian. The atonality of free jazz is often credited by historians and jazz performers to a return to non-tonal music of the nineteenth century, including field hollers, street cries, and jubilees (part of the “return to the roots” element of free jazz). This suggests that perhaps the movement away from tonality was not a conscious effort to devise a formal atonal system, but rather a reflection of the concepts surrounding free jazz. Eventually, jazz became totally “free” by removing all dependence on chord progressions and instead using polytempic and polyrhythmic structures.