He said the unique thing about jazz is group improvisation. When you improvise, it is axiomatic that you take risks and can't foretell results. When five or six musicians improvise simultaneously, the result is even more fortuitious. That is its charm. Something has been developed here that has no duplication.
Jazz is free.
Through spontaneous improvisation, a musician expresses his personality consciously and subconsciously. His music, with its variation of melodic lines and rhythmic patterns, can establish a changing flow of attitudes just as those revealed by a facial expression or a gesture even without words. Without inhibition or the fear of being reprimanded, a soloist rises and speaks without the aid of notes or previous preparation. Speeches with words of various inflections and insinuations are replaced with a flow of melodic, rhythmic music. One soloist will speak for himself on a chosen topic and then retire to hear the feelings of another on the same subject.