Improvisation is the art of becoming sound. It is the only art in which a human being can and must become the music he or she is making. It is the art of constant, attentive and dangerous living in every moment. It is the art of stepping outside of time, disappearing in it, becoming it. It is both the fine art of listening and responding and the more refined art of silence. It is the only musical art where the entire "score" is merely the self and the others, and the space and moment where and when this happens. Improvisation is the only musical art which is predicated entirely on human trust and love. 

The art of improvisation assumes (and for me unequivocably proves) that human beings are musical beings and that not unlike the great natural musicians of the animal kingdom - from crickets and cicadas to whales, wolves and lions - all human beings are born with, possess and participate in some form of music. Regardless of the musical context (the people place or time, tradition or style) the art of improvisation puts the full responsibility for the music being made on the persons making it, and for the entire duration of its making. 

Improvised music is, however, generally based on something: a word, a set of fixed tones, a melody, rhythmic pattern, chordal sequence, timbral change, gesture (crescendo, diminuendo, fragmentation, drone etc), a reaction, a memory, a dream. Or any combination of these. All musical cultures employingforms of improvisation, codify these forms around a specific set of sounds developed through a long historical process. 

The improvisation groups AMM in London and MEV (Musica Elettronica Viva) in Rome, however can be said to have taken the most radical position in regard to this process of "liberation." Musically speaking both groups were attempting to literally reinvent music from zero. What the group MEV essentialy did was to redefine music as a form of property that belonged equally to everyone and hence to encourage its creation freely by and through anyone anywhere. 
(Alvin Curran, 1995)