Their signature sound was based on four-part male/female vocal harmonies arranged by John Phillips, the band?s songwriter who managed to "leave the folk music behind" and blend his writing with the new "beat" sound in an unprecedented mode. On the other hand, The Mamas & the Papas were riven by internal frictions almost from the start which inevitably made them short-lived as a working band. This, as well as other heavily discussed issues like "Who sang and who was edited out from what final mix?" has contributed to the group's myth even forty years later.
From Wikipedia
