Abstract

Human languages, such as French, Cantonese or American Sign Language, are socio- cultural entities. Knowledge of them (`competence') is acquired by exposure to the ap- propriate environment. Languages are maintained and transmitted by acts of speaking and writing; and this is also the means by which languages evolve. The utterances of one generation are processed by their children to form mental grammars, which in some sense summarize, or generalize over, the children's linguistic experiences. These grammars are the basis for the production of a new avalanche of utterances to which the next generation in its turn is subjected. (This picture is simplified, of course, as generations overlap.) Languages inhabit two distinct and separate modes of existence, which have been called (by Chomsky, 1986) `E-Language' and `I-Language'. E-language is the external observable behaviour --- utterances and inscriptions and manifestations of their meanings. E-language is regarded by some as so chaotic and subject to the vicissitudes of everyday human life as to be a poor candidate for systematic study. (E-Language corresponds to what Chomsky, in earlier terminology, called `performance'.) Out of this blooming buzzing confusion the individual child distils an order internal to the mind; the child constructs a coherent systematic set of rules mapping meanings onto forms. This set of rules is the child's I-Language (where `I' is for `internal'). No two individuals' I-Languages have to be the same, although those of people living in the same community will overlap very significantly. But there will usually be at least some slight difference between the I-language features prevalent in one generation and those prevalent in the next. This is the stuff of language evolution, in the sense of the historical development of individual languages, such as Swedish, Navaho or Zulu.