Principles and Methods in Historical PhonologyPicard's methodology has three stages: establishing the sound correspondences between a source language (such as Proto Algonkian) and a target language (such as Arapaho); exploiting the concept of naturalness in phonological change to the fullest in order to construct working hypotheses as to what the most likely historical processes could have been, and to determine in a nonarbitrary fashion which processes could have taken place simultaneously; and