How can a baby learn two languages at the same time?

Article dated March 19, 2024, published in The Conversation online media, as part of the partnership with ENS de Lyon. By Cameron Morin, ATER at ENS de Lyon, affiliated to ICAR Laboratory, Syntax, Meaning and Textuality team. Language acquisition in children is one of the most fascinating features of the human species, as well as one of the most difficult problems in linguistics and cognitive science. What are the processes that enable a child to completely master its native language in just a few years, and to a degree of competence that adult learners of a second language can almost never match? Far from being a matter of consensus, this subject has in fact greatly divided the research communities in these fields: the 20th century was marked by Noam Chomsky's influential idea that native-language acquisition might stem from a universal and innate grammatical faculty in humans , distinguishing them from other animal species. If it's so impressive that a baby can learn even just one language, then how do we explain that it can go on to learn two, three or even more? This question presupposes that bilingualism or multilingualism is sporadic in human societies, the exception rather than the rule. However, not only do experts estimate that almost half the world's population is bilingual , but also that multilingualism is actually more common than monolingualism. Just look at some of the world's most populous countries, such as India and China.