Contemporary study of language has turned to questions of linguistic structure and cognitive psychology of a sort that aroused little interest in the immediately preceding period. The extent to which this is a return to long neglected topics rather than an innovation is not widely appreciated, however, and I would like to comment briefly on this matter here.
A central topic of much current research is what we may call the “creative” aspect of language use, that is, its unboundedness and freedom from stimulus control. The speaker-hearer whose normal use of language is “creative,” in this sense, must have internalized a system of rules that determines the semantic interpretations of an unbounded set of sentences; he must, in other words, be in control of what is now often called a generative grammar of his language. A generative grammar must determine the structural description of each possible sentence, where the structural description of a sentence is a formal object of some sort that contains what information the rules of the language provide concerning the semantic content and phonetic form of this sentence.