Linguistic theory has seen a substantial shift in focus during the past decade. Whereas early research in generative grammar sought descriptive adequacy through the proliferation of transformational rules, recent efforts have concentrated on defining systems of principles that restrict the application of a greatly simplified sys tem of rules of grammar. These principles, because of their broad application within a particular language, and their appearance in a wide range of languages under investigation, are claimed to reflect innate cognitive structures often termed universal grammar....