Proximate and ultimate explanations of individual differences in language use and language acquisition

I evaluate three schools in linguistics (structuralism; generative linguistics; usage based linguistics) from the perspective of Karl Popper’s critical rationalism. Theories (providing proximate explanations) may be falsified at some point in time. In contrast, metatheories, such as Darwin’s theory of evolution and the theory of Language as a Complex Adaptive System (LCAS) (providing ultimate explanations) are falsifiable in principle, but not likely to be falsified. I then argue that LCAS provides a fruitful framework for the explanation of individual differences in language acquisition and use. Unequal frequency distributions of linguistic elements constitute a necessary characteristic of language production, in line with LCAS. However, explaining individual differences implies explaining commonalities (Hulstijn, 2015, 2019). While attributes such as people’s level of education and profession are visible in knowledge of the standard language (declarative knowledge acquired in school), they may be invisible in the spoken vernacular (linguistic cognition shared by all native speakers).