These so-called outliers were difficult to reconcile with the universal grammar that was built on examples from European languages.

Other exceptions to Chomsky’s theory came from the study of “ergative” languages, such as Basque or Urdu, in which the way a sentence subject is used is very different from that in many European languages, again challenging the idea of a universal grammar.

These findings, along with theoretical linguistic work, led Chomsky and his followers to a wholesale revision of the notion of universal grammar during the 1980s.