Recent developments in linguistic theory have led to an important reorientation of research in related fields of linguistic inquiry as well as in linguistics itself. The developments I have in mind, viewed from the point of view of government-binding theory, have to do with the character ization of Universal Grammar (UG) as a set of subtheories, each with its set of central principles (perhaps just one principle central to each subtheory) and parameters (perhaps just one for each principle) according to which a principle can vary between an unmarked ('-') and a marked ('+') para metric value (Chomsky, 1985; 1986). For example, let us assume that there is an X-bar theory in explanation of those features of phrase structure irreducible to other subtheo ries of UG. Within X-bar theory variation among languages is then allowed only with respect to the position the head of a phrase occupies in rela t ion to its complemen ts such that the phrases of a language will be either right- or left-headed. Thus languages will vary between being right-headed in this respect (as in Japanese phrase structure) and being left-headed (as in English phrase structure). Everything else about the phrase structure of particular languages will be fixed within X-bar theory itself or else it will fallout from other subtheories of UG: Case theory; 0-theory, etc. (Chomsky, 1985:161-62; Chomsky, 1986:2-4; and references cited there). Hatters are the same in other modules of grammar.
