As our world grows smaller, and individuals become more mobile thanks to advances in communication and transportation systems, multilingualism has become prominent in both scientific and popular debates. In the past decades, an interesting development in the field has been to measure the cognitive advantages of multilingualism. While such studies are very relevant to understanding consequences of multilingualism on cognition and on the structure of the brain, they contribute to perpetuate the traditional assumption that monolingualism is the default. Speaking one language is perceived as ‘normal’ while mastering more than one is exceptional, and can potentially enhance one’s cognitive capacities.

In this lecture, I take a different perspective: multilingualism is the default. Linguistic theory is primarily concerned with this unique human capacity. Under this view, ‘pure’ monolingualism is exceptional and potentially detrimental to the human multilingual mind. I argue that language acquisition (whether L1 or Ln+1) necessarily involves contact of idiolects of speaker-learners of different profiles acting in different (though sometimes overlapping) socio-cultural contexts. These interactions generate heterogeneous linguistic inputs that are in constant flux, and to which speaker-learners are exposed throughout their lifespan. Such learning contexts can be formally characterized as multilingual (cf. Aboh 2015, 2020), in the sense that speaker-learners, exposed to competing alternatives in the inputs, learn to master multiple ‘registers’ (arguably extensions of different internalized grammars). My working hypothesis is that learning in such a multiple-varieties ecology results from a basic cognitive process: recombination, which enables human learners to merge linguistic features selected from the inputs into new variants. The outputs of recombination are new hybrid linguistic constructs which in turn form the inputs of new generations, hence language change. The proposed view has far-reaching consequences for the study of language.