As the French-Acadian vernacular in Eastern Canada has been dealt with in several linguistic surveys since 1884, including a phonological study by V. Lucci in 1969, Le système phonologique du parler franco-acadien de la region de Moncton, to be published by Didier Press, an approach from the standpoint of diachronic phonology is given here. Research provides illustrations of a few hypotheses regarding phonological evolution, borrowed from Martinet's theory: the importance of assessing functional efficiency, the notion of structure and "phonetic economy." An examination was made of the very distinct and recent influence of extralinguistic factors (schooling, linguistic exchanges with the province of Quebec, French-speaking rural populations moving to cities with a majority of English speakers) wherein the difficulty of identifying explanatory processes and of reconstituting evolutionary sequences is emphasized. These extralinguistic factors set forth a "hastened," almost entirely phonetic evolution which was not followed by an evolution of the phonological system. The alterations affect the arrangement of the old system (disappearance of variants, neutralizations) without causing any phonemic creation or loss. This illustrates one of the principles of functional linguistics: the primacy of distinctive function. Under considerable pressure from sociocultural factors, the language, while altering under the influence of both standard French and English, has allowed the maintenance of linguistic communication between people belonging to different generations. AA