Gavin B.

The differences are fairly clear but brilliant players like Trane, Mingus & Miles frequently blurred the categorical distinctions between regular (traditional) jazz and free jazz. Ornette Coleman, Sun Ra & Eric Dolphy are more firmly entrenched in the pure free jazz tradition. All of the above mentioned players were all masters of the traditional jazz form, regardless of their inclinations toward the free jazz form.

The differences between traditional jazz and free jazz are as follows:

• Traditional jazz is built on a framework of established song forms, such as the 12 bar blues, or the 32 bar form of a popular ballad. In free jazz, the dependence on a fixed and pre-established form is eliminated, and the role of improvisation is correspondingly increased.
  
• Tradtional jazz uses clear defined meters and strongly-pulsed rhythms, usually in 4/4 or (less often) 3/4. Free jazz retains rhythms but often swings without regular meter. The rhythm of free jazz frequently accelerates or slows down depending on the improvised musical direction.
  
• Traditional jazz follows conventional harmonic structures. Free jazz, by definition dispenses with harmonic structures, but free jazz frequently employs combinations of the diatonic, altered dominant and blues phrasing of traditional jazz. In free jazz you may hear dissonant off key playing but it's not because the players are tone deaf...free jazz has a different set of tonal & harmonic ground rules.
  
• The most striking element of free jazz harmonics is the use of Eastern atonal harmonics and polyrhythmic structures that characterize African tribal music, Arabic music and classical raga music from India.

In reality free jazz is not a modern musical form, rather it's an exploration of ancient and more primitive musical forms that predate the more refined and conventionally structured traditional ballad, dance song or 12 bar blues. Many of the ancient forms of free jazz come from tribal cultures that existed long before the discovery of America.

Trumpeter Wynton Marsalis is the ultimate traditional jazz theorist and has made the controversial argument that jazz ended when jazz musicians abandoned the conventional American blues and ballad form & began the free jazz experiment. It's a conservative cultural perspective, but there is some logic behind it because traditional jazz was built on traditional American music forms while free jazz is built on more exotic music forms from Africa, the Middle East and the Far East. For Marsalis, traditional jazz died at the end of the bop era; and free jazz, fusion, & post bop traditions are musical mutations of jazz but not valid forms of traditional American jazz.

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There are two types of music: the first type is the blues and the second type is all the other stuff.
Townes Van Zandt