The Ari people of South-West Ethiopia treat the human voice as a veritable instrument: exploring it's entire acoustic range by varying registers, timbres and vowel resonance; their grand-scale polyphonies are highly sophisticated, yet not without elements of spontaneity and surprise. The period of great collective ceremonies begins at the end of the rainy season - marriages (wochmi), the end of harvesting (buk), funerals (efi) and the lifting of periods of mourning (chi: chi). Participants abandon their habitual activities to devote themselves to the celebration of a decisive life cycle event, amid omnipresent singing and dancing. A strong contrast exists in Ari music between the complexity of the collective polyphonic structure and the sobriety of individual voices. A successful ensemble depends on good combinations of simple elements. Moreover, any apparently rigid polyphonic organization is counterbalanced by a certain flexibility in performance, evident in unpredictable entries of freely moving voices and in a wealth of variations. In Ari polyphonies, a variation is an open proposition, addressed to other musicians, provoking reaction and thereby developing the performance.