In articles about bilingualism and OPOL we usually find two different labels: “one parent – one language” or “one person – one language” which, in my opinion, is a bit misleading.
The term of OPOL was first introduced by the french linguist Maurice Grammont in 1902. In Observations sur le langage des enfants (Observations on Children’s Language), he introduced the idea of une personne, une langue. Literally translated from the French as one person, one language.
He theorized that by separating the languages from the beginning, parents could prevent confusion and code-mixing in their bilingual children. Therefore if each parent speaks only one of the two languages to the child, the chances that the child will mix the languages are reduced. By using his or her own language each parent gives an example of adult language use.
Many studies followed like the one of Jules Ronjat, Le Développement du langage: observé chez un enfant bilingue (The Development of Language: Observations of a Bilingual Child). Observing his son, Louis, Ronjat came to the conclusion that the consistent use of two languages at home from birth on, is a major factor in achieving bilingualism. He noted that Louis had acquired and mastered two languages in a similar phonological order to that of the average monolingual child.
In linguistic circles the term of OPOL is very common and is frequently used in books and articles since the 1980s as a way to describe a child being brought up as a simultaneous bilingual. In these studies we find the word parent alternate with person (cfr. B. Bain and A. Yu, Cognitive consequences of raising children bilingually: One parent, one language, Canadian Journal of Psychology, vol.34(4), Dec. 1980, 304-313). This leads to confusion as the use of parent instead of person implies that the parents are the only linguistic role models for a child.
In my opinion, Grammont’s label one person one language is much more appropriate in our society. It includes also bilingual mum-mum or dad-dad families and families where one parent is absent and another person takes the caregiver-role. Moreover, it does include also other persons in our children’s life like sibilings, extended family, daycarers, nannys, babysitters etc..