The theory of Lexical Phonology, which forms one of the themes of this volume, was developed by Paul Kiparsky and K. P. Mohanan and first introduced in monographs appearing in the early 1980s (Kiparsky 1982a, b; Mohanan 1982). The number of phonologists that have begun to work within or in response to the theory in the short time since its appearance is worthy of remark. One reason that Lexical Phonology has sparked so much interest must surely be that it supplies new tools for analysis and new ways of approaching recalcitrant problems. But another part of its appeal lies in the way it comes as a natural outgrowth of and response to so many of the major trends in phonology and morphology in the last 15 years. Our purpose in writing this introduction is to trace the history of some ideas that come together in Lexical Phonology and to provide the reader with an overview of the model itself. In this we shall be covering some already well-trodden ground, for Kiparsky, Mohanan, and many of their colleagues and students have included eloquent introductions to Lexical Phonology within their articles. However, we trust that readers of the Phonology Yearbook will find it useful to have in hand an exposition of the different facets of the model and the recent challenges and modifications it has undergone. And while our intentions are more pedagogical than critical, we shall from time to time point out difficulties inherent in some or all versions of the model.

At the level of description, this study is concerned with the interaction of the rules of stress assignment in Spanish with rules governing the alternation of certain vowels with diphthongs. The descriptive discussion, in turn, relates primarily to two theoretical questions concerning the lexicon, namely, the role of null phonological segments in lexical representations and the nature of lexical diacritics that control the application of non-automatic phonological rules.

One of the current debates in the theory of Lexical Phonology revolves around the question whether the cyclicity of lexical strata is derived from Universal Grammar or has to be specified in individual grammars. Pesetsky (1979), Mohanan (1982) and Kiparsky (1982) assume that all lexical strata are cyclic. In contrast, Mohanan & Mohanan (1984) and Halle & Mohanan (1985) propose that lexical strata may be either cyclic or noncyclic, and that it is necessary to indicate the cyclicity of each stratum language specifically. Kiparsky (1984) allows the possibility of noncyclic lexical strata, but holds that only the last lexical stratum can be noncyclic, thereby eliminating the need for the specification of cyclicity in grammars

Paul Kiparsky's paper (1982) ‘From Cyclic to Lexical Phonology’ is the most interesting recent development in the line of research originated by Kiparsky (1973) and Mascaró (1976). The major task in this research is the investigation of the ways in which rules apply to phonological structures. Kiparsky (1973) makes the very pointed observation that some phonological rules apply exclusively in derived environments. An environment is derived if either (i) or (ii) is true:

(i) the structure which is relevant to the application of the rule arises at morpheme boundaries: the environment is thus derived morphologically;

(ii) the structure which is relevant to the application of the rule arises in the course of phonological derivation due to the application of an earlier phonological rule: the environment is thus derived phonologically.

One of the most fundamental recurrent issues characterising the development of linguistic theory has been the relative degree and nature of ‘modularisation’ of the various components of the grammar. Two significant developments in recent phonological theory reflect this.

In the past few years a great deal of attention has been paid to the representation of suprasegmental phenomena in phonology, with the resulting development of a number of partly competing theories and models of suprasegmental representation – in particular, various versions of AUTOSEGMENTAL PHONOLOGY (see, for example, Goldsmith 1976; Halle & Vergnaud 1981; Clements & Keyser 1983) and METRICAL PHONOLOGY (Liberman & Prince 1977; Hayes 1980, 1982; Prince 1983; Giegerich 1985). Other frameworks have also been developed which allow for the representation of phenomena in this area, notably that of DEPENDENCY PHONOLOGY (Anderson & Jones 1974, 1977; Ewen 1980; Anderson 1984; Anderson & Ewen 1980, forthcoming).It has, moreover, become obvious that although these theories at first seemed very different, many of the differences are more apparent than real, so that in some respects the proposals are complementary rather than alternative - and in many areas it is clear that we are moving towards a situation where a single model can perhaps be developed from the various frameworks (cf. Leben 1982; Goldsmith this volume).

In this article we have two primary objectives: (1) to elaborate in some detail a theory of phonological representations embedded within a parametric framework, and (2) to apply this theory to a particular vowel system which displays some rather interesting properties. This work is a continuation of a collaboration on a programme of research on phonological theory begun in 1982 (cf. Vergnaud 1982; Kaye & Vergnaud 1984; Kaye et al. 1984, 1985, in preparation).This programme incorporates the view that phonology is to be regarded as a system of universal principles defining the class of human phonological systems. These principles underdetermine given phonologies in certain specific areas. A complete phonological system consists, then, of these principles along with sets of parameter values. Taken together, the principles and language-specific parameter settings give a complete characterisation of the phonological system under study. In this model, a phonological system contains no rule component. The observed phonological phenomena result from a combination of the general principles governing phonological representations and structures and the parameter values in operation in the particular language. We view this line of research as a continuation of the development of a theory of markedness (cf. Chomsky & Halle 1968 (SPE); Kean 1975, 1979). At the moment of writing, this view of phonology remains a long-term objective of our research programme. However, an increasing number of phonological processes which were formerly considered to be manifestations of rules are now successfully derivable from the principles of Universal Phonology (UP) (cf. Kaye & Lowenstamm 1984, to appear).

In the current nonlinear model of CV phonology (Clements & Keyser 1983), phonological representations are organised into several levels or tiers, of which the following three are the most significant: the central CV tier (skeleton), whose units, C and V, are autosegmentally associated with the units of the syllable tier on one end and with the units of the segmental tier on the other. The segmental tier itself is organised into subtiers of distinctive features; the internal structure of the syllable tier is subject to considerable debate in the literature. In addition, CV-level units may be linked to melodies on separate autosegmental tiers in the case of suprasegmental phenomena like tone and vowel harmony.