formal learnability theory the study of human language learning through explicit formal models typically employing artifical languages and simplified learning strategies. The fundamental problem is how a learner is able to arrive at a grammar of a language on the basis of a finite sample of presented sentences (and perhaps other kinds of information as well). The seminal work is by E. Gold (1967), who showed, roughly, that learnability of certain types of grammars from the Chomsky hierarchy by an unbiased learner required the presentation of ungrammatical strings, identified as such, along with grammatical strings. Recent studies have concentrated on other types of grammar (e.g., generative transformational grammars), modes of presentation, and assumptions about learning strategies in an attempt to approximate the actual situation more closely. See also GRAM- MA. R.E.W.