Current crosslinguistic acquisition research reflects varied motivations. Three of these are analyzed as background to a developmental perspective on acquisition across and within languages. Each of the three orientations discussed below has a rather different focus: on mechanisms of acquisition, on endstate grammars, and on linguistic functions and the development of discourse respectively. These concerns are clearly not mutually exclusive, either in principle or practice, but it proves useful to distinguish between them for purposes of exposition.

MECHANISMS AND PRINCIPLES GUIDING ACQUISITION: A CONFLUENCE OF CUES

One major thrust in current research is concerned with psycholinguistic factors underlying the process of acquisition, what have been called ‘mechanisms of language acquisition’ (MacWhinney, 1987). Such mechanisms include ‘the competition model’ (Bates and MacWhinney, 1987; MacWhinney, 1989); a concern with various kinds of ‘bootstrapping’ (Naigles, Gleitman and Gleitman, in press; Pinker, 1984, 1987; Shatz, 1986); as well as extensions of earlier work on acquisitional strategies and principles for relating forms to meanings, such as Eve Clark's (1987, 1988) ‘principle of contrast’ and, most particularly, Slobin's (1973, 1985b) ‘operating principles’. Researchers differ in how committed they are to nativism – i.e. the weight they assign to innate principles and categories compared with the importance of environmental factors such as input, on the one hand, and learner-internal ‘constructivist’ factors, on the other. They also differ in their commitment to modularity – i.e. the extent to which they view language – particularly the syntactic component – as a self-contained or encapsulated domain of knowledge or as bound up with other cognitive domains.