Preface by Chomsky It is about half a century since the study of language undertook a rather new ccurse,while renewing some traditional concerns that had long been neglected.The central change was a shift of attention from behavior and the products of behavior (texis,corpora,etc.to the internal mcchanisms that enter into behavior.This was part of a general shilt of perspective in psychology towards what became known as "cognitive science,and was in fact a significant factor in contributing to this development. With this departure from prevailing structuralist and bchavionst approaches,the objcct of inquiry becomes a property of individual persons, my granddaughters for example.We ask what special properties they have that underlie an obvious but noncthelcss remarkable fact.Exposed to a world of "buzzing,booming confusion"(in William James's classic phrasc),each instantly identified some intricate subpart of it as linguistic,and reflexively, without awarencss or instruction which would be useless in any event), performed analytic operations that led to knowledge of some specific linguistic system.in one case,a variety of wha:is called informally "English,"in another a variety of "Spanish.It could just as casily been one of the Chinese languages,or an aboriginal language of Australia,or some other human language.Exposed to the same environment,their pet cats (or chimpanzees, ete.would not even take the first step of identifying the relevant category of phenomena,just as humans do not identify what a bee perceives as the waggle dance that communicatcs the distance and orientation of a source of honey. All organisms have special subsystems that lead them to deal with their environment in specific ways.Some of these subsystems are called "mental" or "cognitive,"informal designations that need not be made precise,just as there is no need to determine exactly where chemistry ends and biology begins.The development of cognitive systems,like others.is influenced by the environment,but the general course is genctically determined.Changes of nutrition,for example,can have a dramatic offect on development,but will not change a human embryo to a bee or a mouse,and the same holds for cognitive development.The cvidence is strong that among the human cognitive systems is a "faculty of language"(FL),to borrow a traditional term:some subsystem of mostly the brain.The cvidence is also overwhelming that apart from severe pathology,FL is close to uniform for humans:it is a genuine species property.The "initial state"of FL is determined by the common human genctic endowment.Exposed to experience,FL passes through a series of statcs,normally reaching a relatively stable state at about puberty,after which changes are peripheral: growth of vocabulary,primarily. F14